Parallel redundant power distribution

ABSTRACT

Systems and methods are provided for reliable redundant power distribution. Some embodiments include micro Automatic Transfer Switches (micro-ATSs), including various components and techniques for facilitating reliable auto-switching functionality in a small footprint (e.g., less than ten cubic inches, with at least one dimension being less than a standard NEMA rack height). Other embodiments include systems and techniques for integrating a number of micro-ATSs into a parallel auto-switching module for redundant power delivery to a number of devices. Implementations of the parallel auto-switching module are configured to be mounted in, on top of, or on the side of standard equipment racks. Still other embodiments provide power distribution topologies that exploit functionality of the micro-ATSs and/or the parallel micro-ATS modules.

CROSS-REFERENCES

This application is a continuation of and claims priority from U.S.patent application Ser. No. 14/191,339 filed on Feb. 26, 2014, entitled“PARALLEL REDUNDANT POWER DISTRIBUTION,” (U.S. Pat. No. 9,658,665) (“the'339 Application”), which is a nonprovisional of and claims priorityfrom U.S. Patent Application No. 61/798,155, filed on Mar. 15, 2013,entitled, “LOAD BALANCING FOR PARALLEL REDUNDANT POWER DISTRIBUTION,”and which is also a nonprovisional of and claims priority from U.S.Patent Application No. 61/769,688, filed on Feb. 26, 2013, entitled,“PARALLEL REDUNDANT POWER DISTRIBUTION.” In addition, this applicationis a continuation-in-part of U.S. patent application Ser. No. 13/208,333(“the '333 Application”), filed on Aug. 11, 2011, entitled, “PARALLELREDUNDANT POWER DISTRIBUTION” (U.S. Patent Application Publication No.US-2012/0181869-A1), which is a nonprovisional of U.S. ProvisionalPatent Application No. 61/372,752, filed Aug. 11, 2010, entitled “HIGHLYPARALLEL REDUNDANT POWER DISTRIBUTION METHODS,” and from U.S.Provisional Patent Application No. 61/372,756, filed Aug. 11, 2010,entitled “REDUNDANT POWER DISTRIBUTION.” The '333 Application is acontinuation-in-part of U.S. patent application Ser. No. 12/569,733,filed Sep. 29, 2009, entitled “AUTOMATIC TRANSFER SWITCH MODULE” (nowissued as U.S. Pat. No. 8,004,115), which, in turn, is acontinuation-in-part of U.S. patent Ser. No. 12/531,212, entitled“AUTOMATIC TRANSFER SWITCH,” filed on Sep. 14, 2009, which is the U.S.National Stage of PCT Application US2008/57140, entitled “AUTOMATICTRANSFER SWITCH MODULE,” filed on Mar. 14, 2008, which claims priorityfrom U.S. Provisional Application No. 60/894,842, entitled “AUTOMATICTRANSFER SWITCH MODULE,” filed on Mar. 14, 2007. This application is acontinuation-in-part of U.S. patent application Ser. No. 13/108,824,filed on May 16, 2011, entitled, “POWER DISTRIBUTION SYSTEMS ANDMETHODOLOGY” (U.S. Patent Publication No. US-2012/0092811-A1), which iscontinuation of Ser. No. 12/891,500, entitled, “Power DistributionMethodology,” filed on Sep. 27, 2010, which is a continuation-in-part ofInternational Patent Application No. PCT/US2009/038427, entitled, “POWERDISTRIBUTION SYSTEMS AND METHODOLOGY,” filed on Mar. 26, 2009, whichclaims priority from U.S. Provisional Application No. 61/039,716,entitled, “POWER DISTRIBUTION METHODOLOGY,” filed on Mar. 26, 2008. Thecontents of all the above applications are incorporated by referenceherein as set forth in full and priority from these applications isclaimed to the full extent allowed by U.S. law.

FIELD

The present invention relates to the design and operation of powerdistribution systems and, in particular, to parallel redundantdistribution of power including distribution of power to criticalequipment such as in medical contexts or in data center environments.

BACKGROUND

Data centers have a specific set of issues that they must face inrelation to power supply and management. Traditional techniques in thisarea were developed from prior industrial electrical practice in a timewhen a typical data center held very small numbers of mainframecomputers and the change rate was low. Now, data centers often containtens of thousands of electronic data processing (EDP) devices with highrates of change and growth. Data centers are also experiencing rapidlygrowing power capacity demands driven, for example, by centralprocessing unit (CPU) power consumption that is currently increasing ata rate of approximately 1.2 annually. Traditional techniques were notadopted to cope with these change rates, and data centers are thereforehaving great difficulty in scaling to meet those needs.

For example, in a typical data center power distribution network, thebranch distribution circuit is the area where most incidents that resultin a loss of power to a receptacle typically occur. Indeed, this iswhere people tend to make changes in the types and amounts of load.Possibly the most common cause of electrical failure, then, is thebranch circuit breaker being tripped by a person plugging in a load thatexceeds the capacity of the circuit.

In a data center environment, this issue can be complicated in caseswhere there are thousands of branch circuits present. Also, data centerstend to maintain loading of each branch circuit at or below about 75% ofits capacity to account for “inrush loads” that can occur during a coldstart, when all of the connected EDP equipment is powering upsimultaneously (e.g., which may include spinning up fans, disk drives,etc.). This is typically considered as the highest load scenario; and,if not accounted for, it can trip the branch circuit breakers when ithappens. A further contributing factor to this issue is that manyinformation technology (IT) or data center personnel do not always knowthe power demands of the equipment they are installing, especiallyconsidering that the exact configuration in which the equipment isinstalled can vary the power it draws considerably.

One traditional technique that is used to address this issue is powermonitoring. Power monitoring devices (e.g., via plugstrips with amperagemeters or Power Distribution Units (PDUs), wall mounted or free-standingunits which contain distribution circuit breakers that are connected topower whips that power equipment racks on the data center floor) can beused to determine a current power draw. However, for at least thereasons discussed earlier, sudden changes in power draw can cause suddenproblems, which would not be easily remedied by such devices. Forexample, data center staff or users can trip circuit breakers when theyinstall new equipment, potentially causing service interruptions, whichmay not be detected using power monitoring devices in time to preventthe issue.

Another factor that contributes to power distribution issues is thatmany models of EDP equipment have only one power supply, and thereforeone power cord. This tends to be even more typical of medical equipmentand other types of equipment that may often be deployed intomission-critical or life safety roles. However, since they only have onepower input, they can be vulnerable to downtime due to power failures.Also, having only a single power cord and/or supply can complicatemaintenance, which power systems can require from time to time. In fact,this can be true even if multiple independent power sources areavailable, when the device can only be plugged into one power source ata time.

One traditional technique that is used to address this issue is toinstall auto-switching power plugstrips. However, those plugstrips aretypically bulky and expensive. Further, the types that are used in datacenters are usually mounted horizontally in data equipment racks. Thisconfiguration can take up valuable rack space, and tends to take evenmore rack space with its two input plugs connected to two differentpower sources.

SUMMARY

The present invention relates to improved parallel distribution of powerin various contexts including in data center environments. Inparticular, the invention relates to providing improved automatictransfer switches (ATS), for switching between two or more power sources(e.g., due to power failures such as outages or power quality issues),as well as associated power distribution architecture, components andprocesses. Some of the objectives of the invention includes thefollowing:

Providing a high switch density ratio in connection with equipmentracks, such that any failure of a switch will affect a small number of(e.g., one or only a few) pieces of equipment;

Providing a highly redundant, fault-tolerant, scalable, modular parallelswitch design methodology that allows a family of automatic transferswitches in needed form factors to be constructed for a variety ofauto-switching needs in the data center and other environments;

Providing a low switch overhead such that valuable rack space occupiedonly by switches, and not available for equipment, is minimized;

To minimize power cable routing and airflow issues in the data centerequipment rack (2-post) and/or cabinet (4-post) (both of which areencompassed herein by references to as equipment rack or “rack”);

To allow the incorporation of locking power cord technologies at one orboth ends of the power cord for more secure power delivery, for example,in data centers including those located in seismically activegeographies such as California;

To offer an alternate method to maximize the efficiency of usage of datacenter floor space and allow the deployment of the maximum number ofequipment racks;

Providing a compact switch and rack/data center architectures enabled bysuch a compact switch;

Incorporating a variety of power delivery, power receptacle and or powercord outlet management, monitoring and security innovations as describedin U.S. patent application Ser. No. 12/891,500, entitled “PowerDistribution Methodology.” This allows the creation of intelligentauto-switched power distribution methods that incorporate auto-switchingas an integrated feature of the power distribution methodology. This canbe done both with or without the use of in-rack plugstrips that areexternal to the auto-switch in either horizontal or verticalform-factors;

Providing a variety of circuits for enhanced switch performance,including in compact switch designs;

To allow for use of narrower and shallower racks thereby allowing moreefficient use of data center floor space and data center cubic volume;and

Providing coordinated control of multiple (two or more) switches as maybe desired for polyphase power delivery or other reasons.

These objectives and others are addressed in accordance with the presentinvention by providing various systems, components and processes forimproving power distribution. Many aspects of the invention, asdiscussed below, are applicable in a variety of contexts. However, theinvention has particular advantages in connection with data centerapplications. In this regard, the invention provides considerableflexibility in maximizing power distribution efficiency in data centerenvironments. The invention is advantageous in designing the powerdistribution to server farms such as are used by companies such asGoogle or Amazon or cloud computing providers.

In accordance with one aspect of the present invention, a method andapparatus (“utility”) is provided to enable a high switch density at anequipment rack without dedicating substantial rack space to switchunits. A high switch density is desirable so that a malfunction of asingle switch does not affect a large number of EDPs. On the other hand,achieving a high switch density by way of a proliferation ofconventional switch units, that may occupy 1 u of rack space per switch,involves a substantial trade-off in terms of efficient use of rackspace. Various instantiations of automatic transfer switches (ATSs), asdescribed herein, can be implemented using no or little, dedicated rackspace per switch, thus enabling high switch density without any undueburden to rack space.

Accordingly, the noted utility involves an equipment rack having anumber of ports for receiving equipment, e.g., where each port may havea height of 1 u It will be appreciated that some equipment may occupymultiple ports. The equipment rack system includes a number, N, of EDPsmounted in at least some of the ports of the rack and a number, S, ofindependently operating ATSs. Each of the ATSs is configured to receivedinput power from first and second external power sources, to detect apower failure (e.g., a power outage or unacceptable power quality)related to the first external source, and to automatically switch itsoutput power feed to be coupled to the second external source when apower failure related to the first external source is detected.

The noted equipment rack system has a switch density ratio defined asS/N. In addition, the equipment rack system has a switch overhead ratio,defined as a ratio of the number of ports occupied only by ATSs to thenumber of ports collectively occupied by the ATSs and the EDPs is lessthan S/(N+1).

For example, the switch density ratio may be at least 1/4 (and morepreferably at least 1/2), and the switch overhead ratio may be less than1/5 (and more preferably, less than 1/8). In data center environments,it is generally desired to use tall racks so that the floor space of thedata center is efficiently utilized. For example, a rack may have aheight of more than 30 u's and even more than 50 u's in some cases.Moreover, it is generally not desirable to leave many rack spacesunoccupied for the same reason. Accordingly, for practical purposes, itis expected that data centers will often be configured so that EDPsoccupy at least 20 ports of the rack. In such cases, the presentinvention enables high switching densities while occupying no more than2 of the ports with ATSs. For example, multiple ATSs (e.g., 12 or moreATSs) may be disposed in one or more enclosures that are collectivelyoccupy only 1 or 2 u's of the rack. In some implementations describedbelow, more of the rack ports of spaces are dedicated to switching unitsand each piece of equipment can have its own ATSs (i.e., a switchdensity ratio of 1 and a switch overhead ratio of 0).

According to another aspect of the present invention, a utility isprovided for use in supplying redundant parallel power to electronicdata processing system. The utility involves a number of automatictransfer switches disposed within an enclosure sized to fit within asingle standard equipment rack space. Each of the ATSs is configured toreceive a first power feed from a primary power source disposed externalto the enclosure, receive a second parallel power feed from a secondarypower source disposed external to the enclosure, detect a power failureon the first parallel power feed, and automatically switch an outputpower feed from being electrically coupled with the first parallel powerfeed to be electrically coupled with the second parallel power feed whenthe power failure in the first parallel power feed is detected. In thismanner, a number of ATSs can be disposed in a single rack space.

Preferably, the enclosure has a height of no more than approximately 1.5u and may have a height of 1 u, i.e., no more than about 1.75 inches.Moreover, each ATS preferably has a power density of at least about 2kilowatts per 10 cubic inches. In this manner, substantial switchingcapacity can be provided within the spatial-envelope of one or two u'sof a standard rack. In certain embodiments, multiple ATSs may bedisposed in a single housing that may occupy less than two, for example,one u of rack space. For example, 12 or more ATSs, each having a powerdensity of 2 kilowatts can be contained in 1.5 u's of rack space orless. Such embodiments allow for elimination of plugstrips along sideequipment in the racks, thus, allowing for narrower racks and moreefficient use of data center floor space.

According to another aspect of the present invention, a family ofparallel ATS units in a variety of needed capacities and form factorscan be constructed by using a modular construction methodology that iscost-effective to implement and offers the ability to add increasedreliability to the ATS units so constructed. The ATS capability socreated can also be incorporated in a variety of apparatus, for examplesuch as described in U.S. patent application Ser. No. 12/881,500,entitled “Power Distribution Methodology.” This allows the creation ofauto-switched power distribution methods that incorporate auto-switchingas an integrated feature of the power distribution methodology.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described in conjunction with the appendedfigures:

FIG. 1 shows a example of a power distribution topology;

FIG. 2 shows a power distribution designed for a typical data center;

FIG. 3 shows how power efficiencies vary with load changes for doubleconversion UPS units used in data centers;

FIG. 4 shows illustrates the increase in large data centers that uselarge numbers of servers in recent years;

FIG. 5 shows illustrates a switch in accordance with the presentinvention;

FIG. 6 shows examples of a hydra cord;

FIG. 7 shows a system diagram of an illustrative micro-ATS, according tovarious embodiments;

FIG. 8A shows a circuit diagram of an illustrative power supplysubsystem in context of an illustrative “A” & “B” power switchingsubsystem for use in some embodiments of a micro-ATS;

FIG. 8B shows illustrative detail of the 15-volt power supply asnormally supplied by HV through a set of resistors;

FIG. 9 shows a circuit diagram of an illustrative “A” power voltagerange detect subsystem for use in some embodiments of a micro-ATS;

FIG. 10 shows a circuit diagram of an illustrative “A” power loss detectsubsystem for use in some embodiments of a micro-ATS;

FIG. 11 shows a circuit diagram of an illustrative “B” powersynchronization detection subsystem for use in some embodiments of amicro-ATS;

FIG. 12 shows a circuit diagram of an illustrative “A”/“B”synchronization integrator subsystem in context of the “B” powersynchronization detection subsystem and the “A” power loss detectsubsystem for use in some embodiments of a micro-ATS;

FIG. 13 shows a circuit diagram of an illustrative timing controlsubsystem for use in some embodiments of a micro-ATS;

FIG. 14 shows a circuit diagram of an illustrative “A” & “B” powerswitching subsystem for use in some embodiments of a micro-ATS;

FIG. 15 shows a circuit diagram of an illustrative disconnect switchsubsystem for use in some embodiments of a micro-ATS;

FIG. 16 shows a circuit diagram of an illustrative output current detectsubsystem for use in some embodiments of a micro-ATS;

FIG. 17 shows a circuit diagram of an illustrative piezoelectric devicedriver subsystem for use in some embodiments of a micro-ATS;

FIG. 18A shows a power distribution topology having an ATS disposed inthe root nodes of the topology;

FIG. 18B shows another illustrative a power distribution topology havingan ATS disposed further downstream, in the distribution nodes of thetopology;

FIG. 18C shows yet another illustrative a power distribution topologyhaving an ATS disposed even further downstream, in the leaf nodes of thetopology;

FIG. 18D shows still another illustrative a power distribution topologyhaving ATSs disposed still further downstream at the EDP equipment, inthe end leaf nodes of the topology;

FIG. 19 shows an illustrative traditional power distribution topology,according to some prior art embodiments;

FIG. 20 illustrates an efficiency versus load graph for a typicaldouble-conversion UPS unit;

FIG. 21 shows an illustrative power distribution topology, according tovarious embodiments;

FIGS. 22A and 22B show illustrative parallel micro-ATS modules,according to various embodiments;

FIG. 23 shows an illustrative power distribution topology that includesa rack-mounted parallel micro-ATS module, according to variousembodiments:

FIG. 24 shows an illustrative power module with its sub-components thatdemonstrates the modular ATS concept, according to various embodiments:

FIG. 25 shows an illustrative set of assembled power modules thatdemonstrates the modular ATS concept, according to various embodiments;

FIG. 26 shows an illustrative set of power modules combined in a numberof form factors to achieve a variety of amperage capacities, thatdemonstrates the modular ATS concept, according to various embodiments;

FIG. 27 shows an illustrative pair of example ATS designs thatincorporate the modular ATS concept, according to various embodiments;

FIGS. 28A-28D show an illustrative control logic that demonstrates themodular ATS concept, according to various embodiments;

FIGS. 29A-29J show an illustrative control logic that adds faultdetection and management features which demonstrates the modular ATSconcept, according to various embodiments;

FIGS. 30A-30R show an illustrative control logic that adds faultdetection and management features and control logic redundancy whichdemonstrates the modular ATS concept, according to various embodiments;

FIGS. 31A-31E show an illustrative parallel relay load balancing methodthat can be used to provide a highly energy efficient method to insurerelay function, reliability and service lifetime with the modular ATSconcept, and any other device that uses large numbers of parallel relaysto switch power capacities that are much greater than those of eachindividual relay, according to various embodiments;

FIGS. 32-32K show various details and operational modes of possibleinstantiations of a method of dealing with relay skew and/or improvingand controlling relay contact actuation times, according to variousembodiments; and

FIG. 33 shows an example of a data center configuration in accordancewith the present invention.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a second label thatdistinguishes among the similar components. If only the first referencelabel is used in the specification, the description is applicable to anyone of the similar components having the same first reference labelirrespective of the second reference label.

DETAILED DESCRIPTION

The following description is structured in two sections, Section 1discusses the issues involved in data center power distribution andinventive solutions to those problems and Section 2 discusses detailedmethods that can be used to construct an automatic transfer switch withthe characteristics needed to build the inventive solutions described inand associated rack/data center architectures. It should be noted thatthe detailed methods described can also be used for other purposes thanconstructing automatic transfer switches.

I. Background—Power Distribution Reliability & Maintenance Issues

The branch distribution circuit is the area where most incidents thatresult in a loss of power to a receptacle occur. The cause is simple,this is where people make changes in the types and amounts of load. Themost common cause of electrical failure is the branch circuit breakerbeing tripped by a person plugging in a load that exceeds the capacityof the circuit. Recent power reliability studies show that UPS unitfailures are also a significant cause of power failures in data centers.It should be noted that certain UPS failure modes will affect theability of the UPS to pass any electrical current. In a data centerenvironment this issue is complicated by the fact that there can bethousands of branch circuits present. Also, in a data center, eachbranch circuit must usually only be loaded to 75% of its capacity, toaccount for the “inrush load” that occurs during a cold start, when allof the connected electronic data processing (EDP) equipment is poweringup simultaneously, spinning up fans, disk drives, etc. This is thehighest load scenario, and if not accounted for, it will trip the branchcircuit breaker when it happens. A contributing factor to this issue isthat most IT or data center staff do not always know what the powerdemands of the equipment they are installing will be, especially in theexact configuration the equipment has, which can vary the power it drawsconsiderably.

Power monitoring is often used (via plugstrips with amperage meters orPower Distribution Units (wall mounted or free-standing units whichcontain distribution circuit breakers that are connected to power whipsthat power equipment racks on the data center floor) to determine thecurrent power draw. However, for the reasons discussed earlier,frequently data center staff or users can trip circuit breakers whenthey install new equipment, potentially causing service interruptions.

Note: For convenience we will use the term equipment rack to describeboth of the terms “equipment rack” and “equipment cabinet”, which areoften used for 2-post vs. 4-post racks.

A method of increasing power reliability is to use an automatic transferswitch (ATS) at various points in the power distribution topology toprovide for automatic failover from a primary power source to a backuppower source. This is typically done at one of three points in the powerdistribution topology, the panelboard on the wall, where the branchcircuits originate, the end of the branch circuit in the rack where thepower is fed to plugstrips or between the plugstrip and the EDPequipment being powered.

The choice of where to place auto-switching in a power distributiontopology has a number of issues to consider.

1. Domain of failure—This is the number of power receptacles that willbe affected if the ATS fails to function properly. All powerdistribution topologies used in data centers can be considered rootedtree graphs, mathematically speaking.

The closer to the root of the tree the ATS is located, the higher thenumber of power receptacles that will be affected by the actions of thatATS. This is shown in FIG. 1, which shows an example power distributiontopology. For the purposes of this discussion, the root(s) of thegraph(s) of the power distribution topology are “downstream” of the corepower infrastructure. The root(s) start at a UPS unit or a powerdistribution panelboard. In this model the power distribution panel iseither a root or a distribution layer node. The branch circuitsoriginate at the power distribution panel and end at the equipmentracks. At the rack, power is distributed via plugstrips (which areconfusingly also called power distribution units (“PDU”) a term that isoften applied to the panelboard.). The plugstrips may have circuitbreakers in them, also. However, for the purposes of this discussion, wewill use the terms panelboards and plugstrips. It should also be notedthat in the descriptions that follow, ATS units can also be used withbusways instead of or with panelboards. Busways are essentially linearpanelboards. They are commonly used in industrial environments such asproduction lines and they have been adopted for use in data centers. Thebusway is normally installed overhead and parallel to a row of equipmentracks. They function like track lighting, where instead of lights, youinsert tap boxes, which are boxes that connect mechanically andelectrically to the busway and have outlet receptacles, outlet pigtailsor outlet wiring that is hardwired. The outlet boxes usually incorporatecircuit breakers to limit the output(s) of the tap box.

It should be noted that large data centers often have many generatorsand UPS units, since there is a limit to the capacity size you can buyand if you exceed that limit you have to put multiple UPS units in andrun them in parallel. Each UPS in this situation will be a root in thepower distribution topology. Similarly, you will usually use multiplepower distribution panelboards, since they come only so large in powercapacity and number of circuit breaker stations. Also, it is moreefficient to locate your panelboards so as to minimize the average powerwhip length, so you tend to use as many as is practical to accomplishthis. Panelboards are typically located on walls, but in some datacenters, especially very large ones, they can be free-standing unitslocated out on the floor.

ATS switches can be used with panelboards and will switch every branchcircuit in a given panelboard to a secondary power source when theprimary power source fails. However, the primary design issue with thismethodology is if the ATS at the panelboard fails, many EDP devices willbe deprived of power. A typical panelboard has a capacity of 225 KVA,and 84 or 96 circuit breaker stations. This can power approximately upto 40 racks via 28-96 branch circuits (depending on the type and numberof branch circuits and the average number of watts used per rack).Having 40 racks go down due to ATS failure in a data center is a majorhit that can have very serious service impacts. This type of failure hashappened in numerous data centers.

2. Power distribution efficiency—This is the amount of power that is“lost” by the insertion of automatic transfer switches into the powerdistribution system. No automatic transfer switch is 100% efficient,they all have a loss factor. There are two primary types of automatictransfer switches, relay based and solid state based. They havedifferent characteristics with regards to power loss and transfer time.Transfer time between the power sources is important because the powersupplies used in modern EDP equipment can only tolerate very brief powerinterruptions. The Computer and Business Equipment ManufacturersAssociation (CBEMA) guidelines used in power supply design recommend amaximum outage of 20 milliseconds or less. Recently released powersupplies can require even faster switching speeds.

a. Mechanical Relay Based ATS

-   -   These switches use one or more relays to switch between their        input power sources. A relay has two primary loss factors, the        contact area of the relay and if the relay requires power to        keep it in the “on” state, where it is conducting current. The        shape and material of the contacts is carefully chosen and        engineered to minimize resistance across the contacts, yet        minimize or prevent arcing across the contacts when they are        switching. Also, since some arcing may occur in some        circumstances, the contacts must be designed to minimize the        possibility of the arc “welding” the contacts shut, which is        very undesirable.    -   Another design issue is transfer time of the relay. The contacts        are mounted (usually on an armature) so that they can be moved        to accomplish their switching function. The contact mass, shape,        range of motion, mechanical leverage and force used to move the        armature are all relay design issues. The range of motion is        dictated by the gap needed between the contacts to minimize        arcing at the maximum design current level. As the maximum        design current is increased, the gap must also increase. The        mass of the contact must be accelerated by the force applied to        the armature, which has a practical limit. These factors impose        a limit on the amount of current that can be sent through a pair        of contacts and still maintain an acceptable transfer time for        EDP equipment. EDP equipment CBEMA guidelines recommend a        maximum of approximately 20 milliseconds of power outage for        continued operation of modern switched power supplies. If the        mass of the armature and contact gap are too large, the relay        transfer time exceeds this time limit.    -   The innovative methods to reduce relay transfer time described        in U.S. Provisional applications entitled, “ACCELERATED MOTION        RELAY” (U.S. Ser. No. 61/792,738), “HYBRID RELAY” (U.S. Ser. No.        61/798,593), and “SOLID STATE RELAY” (U.S. Ser. No. 61/792,576),        which were filed on Mar. 15, 2013, all of which are hereby        incorporated by reference, can be incorporated into automatic        transfer switches in general and in particular the automatic        transfer switches described and incorporated in this filing and        other devices that use or could use relays which would benefit        from reduced relay transfer time. Use of such methods can also        allow the use of a wider range of relays for a particular        application that must transfer in a given timeframe, an example        would be the use of larger capacity relays (either amperage        capacity and/or voltage capacity) which normally would not        transfer fast enough to be of use.    -   Well designed relay based automatic transfer switches have a        loss factor of about 0.5% or less. They also have power supplies        to power their internal logic that typically use in the range of        12-20 watts in operation.    -   Well designed relay based automatic transfer switches have a        loss factor of about 0.5% or less. They also have power supplies        to power their internal logic that typically use in the range of        12-20 watts in operation.

b. Solid State ATS

-   -   These switches use solid state semiconductors to accomplish        switching between their input power sources and their output        load. They can switch faster than relay based switches, because        they use semi-conductor based switching, not mechanical relays.        However, the semi-conductors have a loss factor and the        efficiency of this type of switch is less than that of a relay        based switch, typically around 1%. Also, they are usually less        reliable, unless they are built with redundant internal failover        capability, which makes them much more expensive. Again, they        also have power supplies to power their internal logic that        typically use in the range of 12-200 watts or more in operation,        depending on the size of the transfer switch, and the level of        redundancy offered by the switch.

3. Rack Space Usage

Rack space in a data center is expensive. The data center infrastructureof generators, UPS units, power distribution, raised floor, computerroom cooling, raised floors, etc. is a very large capital investment anda large ongoing operational expense. 1 U of rack space in a standard 42U equipment cabinet is 2.5% of the space available in that rack. Puttingrack mounted automatic transfer switches in large numbers in equipmentracks uses a lot of rack space, which represents a loss of space thatcan be used for EDP equipment. This is very undesirable, which is onereason it is not done.

It should be noted that the transfer switch(s) that are upstream of theUPS units are part of the core power infrastructure not the powerdistribution. Automatic transfer switching is done in the coreinfrastructure to insure continuity of connection to a valid powersource, such as utility power grid feeds or generators. The transfertime of relay based switches that can handle the power capacitiesrequired in the core infrastructure is too slow to avoid (a time of 20milliseconds or less is recommended for EDP equipment by CBEMAguidelines) shutdown by connected EDP equipment for the reasonsdescribed earlier. This is why transfer switches of this type are placedupstream of the UPS units where the brief power outages that theseswitches create on transfer are covered by the UPS units. The family ofmodular, scalable, parallel ATS switches that we describe as part ofthis disclosure can scale to the needed capacities and possess asufficiently fast transfer time so that they can be used in any point inthe power distribution topology, including the core infrastructure, asignificant advantage. They can incorporate fault-tolerant designfeatures that can increase their reliability significantly, which makethem more suitable for use in the topology at points where the ATSrepresents a single point of failure. This enables the use of powerdistribution topologies that are not used now, which can have advantagesfor the data center. For example, moving an ATS unit located in the coreinfrastructure downstream of the UPS can insure that if the UPS unitfails, power delivery continues, an important advantage.

Large Solid State Transfer switches can be used in the coreinfrastructure, and they are fast enough to switch under the 20millisecond CBEMA guideline. However, they are very expensive and canrepresent a single point of failure. And again, they have an unfavorableloss associated with power flowing through the semiconductor devices.They also are much more vulnerable to catastrophic failure than relaybased transfer switches, a significant drawback.

We will discuss later how it is possible to construct a large capacity,fast, efficient and relatively low cost Automatic Transfer Switch bycombining many smaller Zonit Micro Automatic Transfer Switches inparallel. This can be done in a variety of methods. Some use integratedcontrol logic as needed. The modular, scalable, parallel ATS concept isa methodology that can be used to construct such a switch, and canincorporate the technology and innovations of the Zonit Micro AutomaticTransfer Switch.

II. Invention Overview—Highly Parallel Auto-Switched Power Distribution& Appropriate ATS Designs, Including Highly Redundant, Scalable, ModularATS Designs

A. Highly Parallel Auto-Switched Power Distribution

The solutions we have invented are innovative and provide considerablebenefits. They include a number of power distribution methods thatutilize inventions we have made in creating automatic transfer switches(ATS). The automatic transfer switch we are using as a descriptiveexample, the Zonit Micro Automatic Transfer Switch (μATS™) incorporatesthe inventions described in PCT Application No. PCT/US2008/057140, U.S.Provisional Patent Application No. 60/897,842, and U.S. patentapplication Ser. No. 12/569,733, which are fully incorporated herein byreference.

Current automatic transfer switches have specific limitations thatprevent certain implementations of highly parallel auto-switched powerdistribution methods from being used. They are too inefficient, consumetoo much rack space, and cost too much.

The Zonit μATS™ is very small (4.25″×1.6″×1″<10 cu. inches), veryefficient (<0.2V @ maximum load loss) and requires no rack space, sinceit can be self-mounted on the back of each EDP device or incorporated inthe structure of the rack outside the volume of the rack used to mountEDP equipment or in rack mounted plugstrips or in a in-rack or near-rackPower Distribution Unit, due to its very small form-factor. It should benoted that the μATS™ is small enough that it could be integrated intoEDP equipment also.

This small form factor also helps enable the usage of 24″outside-to-outside width EDP equipment cabinets, which have two keyadvantages, they fit exactly on 2′×2′ raised floor tiles which makesputting in perforated floor tiles to direct air flows easy, since theracks align on the floor tile grid and they saves precious data centerfloor space. This is true since NEMA equipment racks are notstandardized for overall rack width, and the narrower the rack is, themore racks can be fit in a given row length. For example a 24″ rack willsave 3″ over the very common 27″ width racks and that represents oneextra rack for each 8 equipment racks in a row. This is now practicalwith modern EDP equipment, since almost all models now utilize front toback airflow cooling. Side-to-side cooling used to be common, but hasnow almost completely disappeared. The caveat is that there is much lessspace on the side of the 24″ rack for ancillary equipment like verticalplugstrips, automatic transfer switches, etc. so those components mustbe as small a form-factor as is practical so that they can fit into therack.

The μATS™ allows efficient, cost-effective and rack space saving perdevice or near per device (ratios of 1 μATS™ to 1 EDP device or 1 μATS™to a low integer number of EDP devices) highly parallel and highlyefficient auto-switched power distribution methods to be utilized. Itshould be pointed out that the ratio of μATS™ units to EDP equipment canbe selected to optimize several interrelated design constraints,reliability, cost and ease of moving the EDP device in the data center.The 1 to 1 ratio maximizes per device power reliability and ease ofmoving the device while keeping it powered up. Note: This can be donewith a device level ATS, especially one like the μATS™ by doing a “hotwalk” where you move the device by first unplugging one ATS power cord,moving the plug to a new location, unplugging the second ATS power cord,etc. Long extension cords make “hot walks” easier. Ethernet cables canbe unplugged and reinserted without taking a modern operating systemdown and TCP/IP connections will recover when this is done. So, it canand has been done. Obviously, cost can be reduced by using other ratiosthan 1 to 1 for μATS™ units to EDP devices. The limiting factor in thiscase is usually μATS™ power capacity and what raised level of risk thedata center manager is willing to take, since the more devices connectedto any ATS the greater the impact if it fails to function properly.

Traditional Power Distribution Methods

Typical data centers use a power distribution design as shown in FIG. 2.

They use double conversion Uninterruptible Power Supply (UPS) units ormuch more recently, flywheel UPS devices. The best double conversion UPSunits used in data centers have power efficiencies that vary as theirload changes as shown in FIG. 3. They typically average 85-90%efficiency, flywheel UPS units average ˜94% efficiency at typical loadlevels. This level of efficiency was acceptable when power costs werestable, relatively low and the climate impacts of carbon based fuels wasnot fully appreciated. Power is now quickly changing from an inexpensivecommodity to an expensive buy that has substantial economic andenvironmental costs and key implications for national economies andnational security. A traditional UPS powered data center more typicallyhas efficiencies in the 88-92% range, because no data center managerwants to run his UPS units at 100% capacity, since there is no marginfor any needed equipment adds, moves or changes. Also, as is typical,the load between the UPS units is commonly divided so that each hasapproximately ½ the load of the total data center. In this case, neitherUPS can be loaded above 50% since to be redundant, either UPS must beable to take the full load if the other UPS fails. This pushes the UPSefficiency even lower, since each unit will usually not be loaded upabove 40-45% so that the data center manager has some available UPSpower capacity for adds, moves and changes of the EDP equipment in thedata center.

FIG. 4 illustrates an important point. The number of very large datacenters that house extremely high numbers of servers has been on theincrease for the last five years or more. The server deployment numbersare huge. There are a number of commercial organizations today that havein excess of one million servers deployed. With facilities of this scaleand the increasing long-term cost of power, making investments inmaximizing power usage efficiency makes good sense, economically,environmentally and in terms of national security. This issue will bediscussed further as we discuss how to best distribute power in datacenters to their servers and other EPD equipment, it is an importantpoint that needs innovative solutions such as we present.

Servers are currently most cost effective when bought in the “pizza box”form factor. The huge numbers of servers deployed in these data centerscurrently are almost all “commodity” Intel X86 architecture compatibleCPU's. This is what powers most of the large server farms running largeWeb sites, cloud computing running VMWare or other virtualizedsolutions, and high performance computing (HPC) environments. It is themost competitive and commoditized server market segment and offers thebest server “bang-for-the-buck”. This is why it is chosen for theseroles.

Commodity servers have great pressure to be cost competitive, especiallyas regards their initial purchase price. This in turn influences themanufacturers product manager to choose the lowest cost power supplysolution, potentially at the expense of best power efficiency, an issuethat has impacts that will be discussed further below.

Data Center Size and Server Counts

There are several reasons to put multiple (dual or N+1 are the mostcommon configurations) power supplies into EDP equipment. The first isto eliminate a single point of failure through redundancy. However,modern power supplies are very reliable with Mean Time Between Failure(MTBF) values of about 100,000 hours=11.2 years, well beyond the typicalservice life of the EDP equipment. The second reason that multiple powersupplies are used is to allow connection to more than one branchcircuit. This is the most common point of failure for powerdistribution, as discussed earlier. Also, having dual power connectionsmakes power system maintenance much easier, by allowing one power sourceto be shut down without affecting end user EDP equipment. However,putting multiple power supplies in EDP equipment has costs. Theadditional power supply(s) cost money to buy. They are almost alwaysspecific to each generation of equipment, and therefore must be replacedin each new generation of equipment, which for servers can be as shortas three years in some organizations.

Power supplies also have a loss factor, they are not 100% efficient andthe least expensive way to make a power supply is to design it to runmost efficiently at a given load range typically +−20% of the optimumexpected load. Power supplies have an efficiency curve that is similarto UPS units, such as was shown in FIG. 2. This presents another issue.The product manager for the server manufacturer may sell that server intwo configurations, with one or two power supplies. In that case, he maychoose to specify only one power supply model, since to stock, sell andservice two models is more expensive than one model of power supply.This trades capital expense (the server manufacturer can sell, theserver at a lower initial price point) vs. operational expense. This isbecause with two AC to DC power supplies, the DC output bus will almostalways be a common shared passive bus in the class of commodity serverthat is most often used in large scale deployments. Adding power sourceswitching to this class of server to gain back efficiency (only onepower supply at a time takes the load) is generally too expensive forthe market being served. It also adds another potential point of failurethat costs to make redundant if needed for greater reliability.

Typical Modern EDP power supplies are almost all auto-ranging (accept110-240V input) and all switched (Draw on the Alternating Current [AC]input power for just a short period of time and then convert this energyto Direct Current [DC], then repeat). Power supplies of this type aremore resistant to power quality problems, because they only need to“drink” one gulp at a time, not continuously. If the input AC powervoltage range is controlled within a known range, they will functionvery reliably. They do not require perfect input AC waveforms to workwell. All that is necessary is that they receive sufficient energy ineach “gulp” and that the input power is within the limits of theirvoltage range tolerance. This makes it possible to use a data centerpower distribution system that is much more efficient than a fully UPSsupplied power system at a very reasonable capital expense.

Very efficient power distribution using highly parallel automatictransfer switching

The primary source of loss in traditional data center power systems isthe UPS unit(s). Conversion losses are the culprit as we discussedearlier. It is possible to avoid these losses by using filtered utilityline power, but this brings a set of issues that need to be solved forthis methodology to be practical that are discussed below. Such a designis shown below in FIG. 5. The power filtering is done by a TransientVoltage Surge Suppression (TVSS) unit, a very efficient (99.9%+) andmature technology.

a. Input Voltage Range Control

-   -   Modern power supplies can tolerate a wide range of power quality        flaws, but the one thing that they cannot survive is input power        over-voltage for too long. A TVSS Unit will filter transient        surges and spikes, but it does not compensate for long periods        of input power over-voltage, these are passed through. To guard        against this possibility, the data center power system we are        discussing must deal with out of range voltage (since modern        power supplies are not damaged by under-voltage but will        shutdown) by switching to the conditioned UPS power if the        utility line power voltage goes out of range. We are going to        discuss two ways to do this. Voltage sensing and auto-switching        could be put in at other points in the data center power system,        but for the reasons discussed earlier, the options we present        are the most feasible.    -   The first place that over-voltage protection can be implemented        is at the utility step-down transformer. Auto-ranging        transformers of this type are available and can be ordered from        utility companies. They have a set of taps on their output coil        and automatically switch between them as needed to control their        output voltage to a specified range. Step-down transformers of        this type of this type are not usually deployed for cost reasons        by utility companies, but they can be specified and retrofitted        if needed.    -   The second place in the data center power system that        over-voltage protection can be implemented is at an ATS in the        power distribution topology. This can be done at the ATS at a        panelboard or at an ATS at the end of a branch circuit, or at an        ATS at the device level. The last is what we chose for reasons        that are discussed later. It should be noted that a        semiconductor based ATS could be used upstream of the UPS, but        this is very expensive and the results of a failure of the ATS        are potentially catastrophic, all of the powered EDP units could        have their power supplies damaged or destroyed if the ATS unit        fails to switch. This is a large downside to chance.

b. Auto-Switching of all Single Power Supply (or Cord) EDP Devices

-   -   If utility line power fails, all single power supply EDP devices        must be switched to a reliable alternate power source, such as a        UPS. This must be done quickly, within the CBEMA 20 millisecond        guideline. Plugging all of these devices directly into the UPS        solves the reliable power issue, but defeats the goal of raising        power distribution efficiency by only using the UPS during the        times when utility power is down. This is especially important        in large server farms, where the cost constraints are such that        single power supply configurations for the massive number of        servers are greatly preferred for cost and efficiency reasons        and services will not be much or at all interrupted by the loss        of a single or a few servers.

c. Auto-Switching of all Dual (or N+1) Power Supply in EDP Devices

-   -   Almost all EDP devices share the load among all available power        supplies in the device. It is possible to build an EDP device        that switches the load between power supplies, so that only one        or more are the active supplies and the others are idle, but as        described earlier, this is rarely done for both cost and        reliability reasons. To insure that multi-power supply EDP        devices draw on only filtered utility line power if it is        available and switch to the UPS if it is not, each of the        secondary power supply units needs to be auto-switched between        the utility line and UPS unit(s). Otherwise, the UPS unit will        bear a portion of the data center load, lowering the overall        efficiency of the power distribution.

d. Avoidance of Harmonic Reinforcing Power Load Surges

-   -   If utility line power fails, all EDP devices must draw on the        UPS unit until the generator starts and stabilizes. Modern        generators used in data centers have very sophisticated        electronics controlling their engine “throttle”. The control        logic of the generator is designed to produce maximum stability        and optimum efficiency. However, it takes a certain amount of        time to respond to a changed electrical load and then stabilize        at that new load. If the load put on the generator changes too        fast in a repeating oscillation pattern, it is possible to        destabilize the generator, by defeating its control logic and        forcing it to try to match the oscillations of the power        demands. This can either damage the generator or force it to        shutdown to protect itself. In either case the data center can        potentially go off-line, a very undesirable result. There are        several potential scenarios that can potentially cause this        problem.

f. Intermittent Utility Line Failure

-   -   Utility line power is outside the control of the data center        operator. It can be affected by weather, equipment faults, human        error and other conditions. It can fail intermittently which        poses a potential hazard to the core data center power        infrastructure. If utility power goes on & off intermittently        and the timing of the on-off cycles is within a certain range,        auto-switching between the utility line source and the generator        (even filtered by the UPS units) can result in harmonic        reinforcing power load surges being imposed on the generator.        This can happens as follows:    -   i. The utility line power fails    -   ii. Power is switched to UPS    -   iii. A timeout occurs and the generator is auto-started    -   iv. The generator stabilizes and is switched into the system,        feeding the UPS    -   v. The utility line power returns, then goes off again    -   vi. The generator will not have shutdown, but the core ATS        switches may now switch between the generator and utility line        sources.    -   The end-user equipment ATS units will return to line power when        it is back on. The timing of this return is a crucial issue. If        it happens too fast for the generator to respond properly, and        utility line power fails in an oscillating fashion, then the        generator can be destabilized as described earlier.

g. Load/Voltage Oscillation

-   -   When a load is switched onto the generator, especially a large        load, its output voltage momentarily sags. It then compensates        by increasing throttle volume and subsequent engine torque,        which increases output current and voltage. There are mechanisms        to keep the output voltage in a desired range, but they can be        defeated by a load that is switched in and out at just the right        range of harmonic frequency. This can happen if the power        distribution system has protection from overvoltage built into        it via mechanisms we will discuss later. The end result can be        harmonic reinforcing power load surges being imposed on the        generator. This can happens as follows:        -   i. The utility line power fails        -   ii. Power is switched to UPS        -   iii. A timeout occurs and the generator is auto-started        -   iv. The generator stabilizes and is switched into the            system, feeding the utility line power side of the system.            Note: This is done in preference to feeding through the UPS            in order to maintain redundant feeds to the racks w/EDP            equipment.        -   v. The generator sags under the large load suddenly placed            on it. It then responds to the load by increasing its            throttle setting.        -   vi. The generator overshoots the high voltage cutoff value            of the highly parallel ATS units and they switch back to UPS            removing the load from the generator.        -   vii. The generator then throttles back and its output            voltage returns to normal levels.        -   viii. The highly parallel ATS units switch back to the            generator, causing it to sag again.    -   Steps vi-viii repeat and can cause a harmonic reinforcing power        load surge to build up and destabilize the generator.

We have now identified four issues that must be solved to be able tosafely, reliably and economically use filtered utility line power.

-   -   1. Input Line power voltage range control    -   2. Auto-switching of single power cord EDP devices    -   3. Auto-switching of dual or N+1 power supply EDP devices    -   4. Prevention of Harmonic Reinforcing Load Surges

One solution that we have selected for these problems is to auto-switchat the device or near device level in the power distribution topology.This solution has a number of benefits over other methods ofauto-switching which will be discussed, but requires an automatictransfer switch with specific characteristics. The chosen auto-switchneeds to have the following qualities.

Must prefer and select the primary power source when it is available andof sufficient quality. This is required. For the power distributionsystem we are discussing, if utility line power is available and ofsufficient quality, you want all loads put on it, for maximumefficiency.

Must protect against out of range voltage on primary power source andswitch to secondary power source if primary power source is out ofrange. It is also desirable, but not required that if the primary powersource has other quality issues, that the ATS switch to the secondary(UPS) power source as a precaution. As noted earlier, this is notrequired, modern power supplies are relatively immune to any powerquality issues except input voltage range, but it doesn't hurt to playit safe.

Must transfer within the CBEMA 20 millisecond limit in both directions,primary to backup power source and backup to primary power source.

Must incorporate a delay factor in B to A switching (except if the Bpower source fails) to prevent Harmonic Reinforcing Load Surges. Thedelay factor chosen must be sufficient to allow modern generators tostabilize their throttle settings and not oscillate.

Should maximize the space efficiency of use of the data center floorspace. There are two ways to look at this issue, maximize the efficiencyof the dimensions of the equipment rack and/or maximize the efficiencyof the use of the volume of space the rack provides for mounting EDPequipment. This involves consideration of several factors.

a. EDP Equipment Rack Dimensions

-   -   Standard NEMA racks are only standardized in one dimension, the        width of the equipment that is mounted in the rack as reflected        in the spacing of the vertical mounting flanges used in the rack        (and the spacing of the fastener holes in those vertical        mounting flanges). They are not standardized for total overall        width, height or depth.    -   The height is generally limited by stability issues, with around        50 U (1 U=1.75″) being near the practical limit, without special        bracing to prevent rack tip-over. The depth is generally limited        to what the projected maximum depth of the mounted EDP equipment        will be. The current maximum depth of most EDP equipment is        around 36″ with a few exceptions. The overall width of the rack        is dependent on what kinds of cabling, power distribution        devices and sometimes cooling devices the rack designer may want        to support mounting on the sides of the rack, outside the volume        occupied by EPD equipment mounted in the rack. The NEMA standard        equipment width that is most commonly used is 19″.    -   Most NEMA standard racks for 19″ equipment are around 27″ wide        to allow adequate space to mount a variety of vertical        plugstrips in the sides of the rack. These plugstrips (also        sometimes called power distribution units) do not have industry        standardized dimensions, so it is difficult for equipment rack        manufactures to optimize their rack dimensions for all available        vertical plugstrips. Therefore the total width and depth of the        rack determine its floor area usage. By eliminating the need to        run anything but power cords and network cords down the sides of        the rack (or optionally down the back of the rack), it is        possible to specify narrower racks, down to a width of        approximately 21″. This is more space efficient. If for example,        24″ racks (which align nicely onto the 2′×2′ floor tiles used in        most raised floors) are used vs. 27″ racks, then one additional        24″ rack can be deployed in a row of 8 racks. This is a        significant gain in data center floor space utilization.    -   It should be pointed out that to use this approach the data        center designer must select racks with appropriate dimensions,        so this is most easily done during initial build out or when an        extensive remodel is being executed.

b. Usage of Equipment Mounting Volume within the Rack.

-   -   Another approach is to not use any of the rack volume that could        be used for EDP equipment. This means that the ATS should mount        in a zero-U fashion or otherwise be integrated into or near the        rack without using rack space that could be used to mount EDP        equipment. It could be integrated into EDP equipment directly.        It could also be integrated into plugstrips or in-rack or        near-rack power distribution units such as the Zonit Power        Distribution Unit (ZPDU), which trades a slight amount of rack        space usage against access at the rack to the circuit breakers        controlling power to the plugstrips in the racks. In this case        the ATS function must be integrated into every sub-branch output        of the ZPDU, so that each one is auto-switched. This is a        potentially worthwhile trade-off to some data center managers.        As discussed earlier, rack space is very expensive. It is not        cost effective to use it for device level ATS units.    -   c. Must be very, very efficient. When deploying ATS units at the        device level, there will be a large number of them. So, they        must be very efficient or they will consume more power than they        are worth to implement. Which leads to the last needed        characteristic.    -   d. They must be relatively inexpensive to buy. This has two        aspects, how much does each one cost, and how long will it last.        Both determine the cost efficiency of the ATS chosen.    -   e. Must be highly reliable. This is required, or the power        distribution design will not be feasible to implement.

The Zonit μATS™ has all of the needed qualities. Its design is specificto that set of requirements, and incorporates patent pending means ofaccomplishing each of those requirements.

-   -   Prefers Primary Source    -   The μATS™ is designed to always use the primary power source if        it is available and of sufficient quality    -   Input Voltage Range Control    -   The μATS™ monitors voltage on the primary input and switches to        the secondary source if it is out of range. It switches back to        the primary source when it returns to the acceptable range and        is stable.    -   Switches between power sources within the CBEMA 20 ms guideline    -   The μATS™ switches from A to B in 14-16 milliseconds. Faster        switching times are can be achieved, but the times chosen        maximize rejection of false conditions that could initiate a        transfer. The B to A transfer times are approximately 5        milliseconds once initiated. This is possible because most B to        A transfers occur after A power has returned and therefore the        μATS™ can pick the time to make the transfer, both power sources        are up and running.

It should be noted that the μATS™ “spreads” the load on the source beingtransferred. This is by design. A population of μATS™ units will have asmall degree of variability in their timing of transfers from the Bsource to the A source, which is not much in real time but issignificant in electrical event time. This variance “spreads” the loadbeing transferred as seen by the power source, for example a generatoror UPS unit. This is because the load appears as a large number of μATS™transfers in a time window to the power source. This is beneficial togenerators and UPS units, since it distributes a large number of smallerloads over a period of time, thus reducing the instantaneous inrush.This is another advantage of our power distribution method.

-   -   Prevents Harmonic Reinforcing Load Surges.    -   The μATS™ waits a specified time constant when on B power before        transferring back to A power (unless B power fails, then it        transfers immediately to A power). The time is selected to be        outside of the normal response time characteristics of most        typical generators. This prevents Harmonic Reinforcing Load        Surges because the generator has time to adapt to the load        change and stabilize its output.    -   Must not use any rack space that could be used by EDP equipment    -   The μATS™ is a very small form factor. It can implemented as a        self mounting device that fits onto a 1 U EDP device as shown in        U.S. patent application Ser. No. 12/569,733, which is        incorporated herein by reference. It can be deployed as a true        “zero U” solution.    -   Must be very, very efficient    -   The μATS™ is extremely efficient, using less than 100 milliwatts        when on the primary power source in normal operational mode.    -   Must be inexpensive and long-lived    -   The μATS™ is very inexpensive to make. It design is such that        its expected useful lifetime is 20 years or more and this could        easily be extended to 35 years+ by using components with longer        lifetimes, which would raise the cost slightly but could be a        worthwhile tradeoff.    -   The μATS™ is moved from each generation of deployed EDP        equipment to the next deployed generation and will return a very        low annual amortized cost over its expected service lifetime.    -   Must be highly reliable    -   The μATS™ is very reliable. This is a requirement and also a        consequence of designing the device for a very long service        lifetime.

We can now discuss the advantages of auto-switching at the device ornear device level vs. auto-switching at other points in the powerdistribution topology. As noted the μATS™ makes switching at the deviceor near device level both possible and desirable. The advantages aredescribed and detailed below.

-   -   Reliability    -   This is easy to understand. A population of highly reliable ATS        units at the device level produces much higher per device power        reliability levels than a traditional ATS that switches a branch        circuit or an entire panelboard can due to the statistics        involved. The chances of all of the μATS™ units failing at the        same time and therefore affecting all of the auto-switched EDP        devices is infinitesimal vs. the chance of an ATS that is at a        closer to the root of the power distribution topology failing.        Consider the following example.        -   1 Panelboard ATS with an MTBF of 200,000 hours        -   1/200000=5.0e-06 chance of failure in any given hour.        -   Note: This would be a very expensive unit w/this MTBF #.        -   200 μATS™ units each unit with an MTBF of 200,000 hours        -   1/200000=0.005% chance of failure per unit in any given hour            and the chance of 200 units failing simultaneously        -   =200,000 raised to the 200th power divided by 1        -   =6.223015277861141707e-1061.    -   This is essentially zero chance of simultaneous failure and is        over 1000 orders of magnitude better than a single ATS with a        200,000 hour MTBF. For a single ATS to achieve reliability        numbers comparable to the massively parallel μATS™ solution, it        would have to be a much more reliable device than 200,000 hours        MTBF.    -   This is a key advantage of the data center power distribution        method we are describing. Reliability is so very important to        data center operators, especially for companies that measure        their downtime in hundreds or thousands or millions of dollars        per hour. It is hard to over-emphasize this point.    -   Efficiency    -   Any method for data center power distribution, especially for        large server farms, must be efficient. The rising cost and        important consequences of power guarantee this. A highly        parallel, device or near device level auto-switched power        distribution method will be the most efficient method that is        cost-effective to implement. There are several reasons for this.    -   Cumulative Contact Area    -   As noted earlier, mechanical relay based automatic transfer        switches are more efficient and at a given cost level, more        reliable than solid-state based automatic transfer switches. As        also discussed earlier, their highest point of loss is usually        contact resistance. This can be minimized with good relay        contact design practices, and increasing the size of the        contacts helps, but there are limits to what can be        accomplished. Another limitation that was discussed earlier is        relay transfer time. This limits the capacity of the relays that        can be used and still stay within the 20 millisecond CBEMA        guidelines.    -   Using many ATS units in parallel at the device or near device        level vs. ATS switches closer to the root of the power        distribution helps to address these limitations and increase        power distribution efficiency. This is because many ATS units        working in parallel have a cumulative relay contact area that is        much greater than is feasible to put in a higher capacity relay        based ATS unit regardless of where that unit is placed in the        power distribution topology. The ATS units in parallel also can        easily have a quick enough transfer time because they use        smaller relay contacts with quicker transfer times. The modular,        scalable, parallel ATS design methodology also can have a quick        enough transfer time.    -   Zonit μATS™ Efficiency    -   Another reason for the greater efficiency of the design is the        features of the Zonit μATS™. The low power consumption feature        is fully described in U.S. Pat. No. 8,004,115 and the        applications from which it claims priority. This is crucial to        being able to implement the described power distribution        methodology. The μATS™ is a more efficient than traditional ATS        units of the same power handling capacity by a factor of 10 or        more. This is a required characteristic to make highly parallel        auto-switched power distribution practical. Otherwise the net        result would be to consume more power not less, regardless of        the capital expense of the switching units used. The modular,        scalable, parallel ATS design methodology also has the ability        to have a very high power efficiency, relative to traditional        ATS units.    -   Cost-Effectiveness    -   Any data center power distribution design must be cost effective        before it will be widely used and accepted. Traditional accepted        methods must be improved upon before they are replaced. The low        manufacturing cost of the μATS™ (relative to current ATS units        of equivalent capacity) and very long service lifetime make it        economically practical to build a highly parallel auto-switched        power distribution system. The modular, scalable, parallel ATS        design methodology implements the benefits of using many μATS™        units in parallel in a potentially even more cost-effective way.    -   Rack Space Usage    -   The space in a data center equipment rack or cabinet is very        expensive, a point that we covered earlier. The μATS™ does not        consume any rack space and is small enough to be integrated into        the rack structure outside of the volume in the rack where EDP        equipment is mounted. As an example consider the following        scenario. A large server farm in a data center often will        consist of many “pizza-box” servers in a rack with perhaps a        network switch. Each server may use ˜3-6 watts of 120V power.        This means that a 15 A ATS can only handle 2-4 servers. If the        ATS units are 1 U rack mounted devices, then using the median        value of 3 servers per 15 A ATS, 25% of the rack space devoted        to servers would be consumed by ATS devices! This is too        inefficient a use of expensive rack space to be practical.

a) Optimized Rack Dimensions

-   -   An alternative approach to efficient use of the data center        floor space that was discussed earlier is to minimize the        dimensions of the rack itself. This can be done in the following        way. At a high level, this approach takes the Zonit        auto-switching technology and deploys it using a different        mechanical packaging method, which has several design benefits        and some design tradeoffs, compared to the methods described in        this and the incorporated filings. The objectives of the present        invention include the following:        -   To minimize power cable count and routing issues, thereby            improving airflow efficiency in the data center equipment            rack (2-post) and/or cabinet (4-post) [hereafter both will            be referenced in the text as equipment rack].        -   To allow the incorporation of locking power cord            technologies at one or both ends of the power cord for more            secure power delivery, for example in data centers located            in seismically active geographies such as California.        -   To offer an alternate method to maximize the efficiency of            usage of data center floor space and allow the deployment of            the maximum number of equipment racks.

These objectives and others are addressed in accordance with the presentinvention by providing various systems, components and processes forimproving power distribution. Many aspects of the invention, asdiscussed below, are applicable in a variety of contexts. However, theinvention has particular advantages in connection with data centerapplications. In this regard, the invention provides considerableflexibility in maximizing power distribution efficiency in data centerenvironments. The invention is advantageous in designing the powerdistribution to server farms such as are used by companies such asGoogle or Amazon or cloud computing providers and others.

In accordance with one aspect of the present invention, a method andapparatus are provided for distributing power via receptacles (orhard-wired output cords) as is shown in FIG. 5. This apparatus has twopower inputs, one from an “A” source, the other from a “B” source. Theamperage of the “A” and “B” power sources can be chosen to match thenumber of auto-switched output receptacles and their anticipated averageand/or maximum power draw. The apparatus takes input power from the “A”and “B” sources and distributes it to a number of Zonit Micro AutomaticTransfer Switch Modules contained in the enclosure (either as separatelydeployed modules or modules combined onto one or more printed circuitboards) of the apparatus. The “A” and “B” power sources may be singlephase, split-phase or three-phase, but in a preferred instantiation,both would be identical. Each of the Zonit Micro Automatic TransferSwitch Modules feeds an output receptacle (or hard wired power cord)located on the face of the enclosure of the apparatus. Two or morecircuit breakers, optionally with visual power status indicators, may beprovided to allow disconnecting the unit electrically from the branchcircuits that feed it. Additional “Virtual Circuit Breaker” controlswitches and indicators may also be included to provide a means todisconnect end-user equipment from individual Zonit Automatic TransferSwitch modules. The apparatus can be mounted within the rack or on topof it or on its side. The size of the enclosure can be minimized due tothe very small form factor of the Zonit Micro Automatic Transfer Switch.It can contain a multiplicity of Zonit Micro Automatic Transfer Switch(“Zonit μATS”) modules within an enclosure that is no more than two NEMAstandard rack units (1 U=1.75″) in height. For example, 12 or more ATSs,each having a power density of 2 kilowatts per 10 cubic inches can bedisposed within 1.5 u's of the rack. The Zonit μATS modules can beconstructed as separate or combined circuit boards to optimize ease andcost of manufacture. Although the enclosure takes up rack space, byeliminating the need for in rack plugstrips, which are usually mountedvertically in the rack, data center floor space can be optimized asfollows. The NEMA standard equipment width that is most commonly used is19″.

Most NEMA standard racks for 19″ equipment are around 27″ wide to allowadequate space to mount a variety of vertical plugstrips in the sides ofthe rack. These plugstrips (also sometimes called power distributionunits) do not have industry standardized dimensions, so it is difficultfor equipment rack manufactures to optimize their rack dimensions forall available vertical plugstrips. Therefore the total width and depthof the rack determine it's floor area usage. By eliminating the need torun anything but power cords and network cords down the sides of therack (or optionally down the back of the rack), it is possible tospecify narrower racks, down to a width of approximately 21″. This ismore space efficient. If for example, 24″ racks (which align nicely ontothe 2′×2′ floor tiles used in most raised floors) are used vs. 27″racks, then one additional 24″ rack can be deployed in a row of 8 racks.This is a significant gain in data center floor space utilization.

In accordance with another aspect of the present invention, a multi-headpower cord “hydra cord” can be provided. This cord can be hardwired intothe apparatus shown in FIG. 5 or receptacles can be provided. An exampleis shown in FIG. 6. The number of output heads on the hydra cord can bevaried to match the desired average power output (or summed power outputto a chosen set of end-user devices) to each connected end-user device.The length and gauge of the hydra power cord (both the main feed sectionand the separate feeds to each “hydra head”) can be optimized tominimize electrical transmission losses and power cord tangle byoptimizing the cord lengths for each hydra cord to supply power to aparticular set of equipment positions in the equipment rack. A set ofappropriately sized hydra cables can be used to feed each equipmentlocation in the rack at whatever interval is desired, such as oneuniform equipment mounting space “1 U” of 1.75 vertical inches. Thepattern of which heads from which hydra cords feed which “U” positionsin the rack can also be varied to control which power phase and sourcefeed each “U” positions for whatever reason is desired, for example tobalance power phase usage. This is an example usage of the technologydescribed in U.S. Pat. No. 6,628,009 the contents of which areincorporated herein as if set forth in full.

In accordance with another aspect of the present invention, lockingpower cord technologies can be used to improve the security of powerdelivery. The apparatus could for example, be equipped with standardNEMA L5-15 locking receptacles for 120V service or NEMA L6-15receptacles for 200V+ service. Other locking receptacle types could beused. The “hydra cord head” on the output cords can be equipped with IEClocking technologies (IEC C13 and C19 would be the types most commonlyused in IT equipment) using the technologies described in PCTApplications PCT/US2008/057149 and PCT/US2010/050548 andPCT/US2012/054518 the contents of which are incorporated herein as ifset forth in full.

In accordance with another aspect of the present invention, theapparatus described can be incorporated in the technologies described inU.S. Pat. No. 6,628,009 and PCT Applications PCT/US2008/057140 andPCT/US2010/050550 the contents of which are incorporated herein as ifset forth in full. This apparatus incorporates the parallelauto-switching functionality in an instantiation of the Zonit PowerDistribution System a novel implementation of which is shown in U.S.Pat. No. 6,628,009. To auto-switch polyphase power sources, a preferredinstantiation would adopt the rule “if one phase of a polyphase powersource fails, all phases switch to the alternate power source”. To dothis the logic each of the single-phase automatic transfer switcheswould be modified to achieve this functionality.

An additional possible refinement would be to use two (or more) μATSmodules to monitor each of the phases of the polyphase power source. Thetwo (or more) modules would act as primary and backup logic fordetermining when to switch the relays (of which there would normallyonly be one set of relays per power phase of the polyphase power source)from the A to the B power source and back from B to A. Anotherpossibility is to use more than two modules and use a majority approachto decide when to switch the relays (of which there would normally onlybe on set of relays per power phase of the polyphase power source) fromthe A to the B power source and back from B to A. An example would be touse three modules and set the logic such that at least two of threeagree to switch power sources before the switch can be made. Theadvantage of these “multi-μATS” approaches is that they eliminate singlepoints of failure in the polyphase switching apparatus.

In accordance with one aspect of the present invention a method forefficiently implementing a family of modular, scalable, optionallyfault-tolerant, parallel ATS units in a variety of form factors isdisclosed. This aspect of the invention describes one possibleinstantiation of how to implement the desired ATS functionality andhighly parallel power distribution methods already discussed. The ATSunits constructed from this methodology can span a wide range of powercapacities and be used at any point needed in the power distributiontopology of the data center. They all can possess a sufficiently quicktransfer time to be compatible with EDP equipment if that is a designrequirement. Another important feature of a modular parallel ATSdesigned with this methodology is that it can be highly fault-tolerantand contain hot-swappable sub-components that can be replaced in theevent of failure. (This is a very important feature, because it lowersthe mean-time-to-repair of the parallel ATS to functionally zero, sinceit never needs to come out of service for repair of sub-assemblyfailures. This matches the need for 7×24×365 service level availabilitywithout downtime that modern data centers need).

Turning to FIG. 25, an illustrative example of a power moduleconstructed in accordance with the present invention is displayed. A PCBboard 2500 that contains a number of relays 2501 and a varistor 2502.The thermistor discussed later in this document for inrush control isnot shown, but could be integrated on the board. Note that the numberand specification of the relays chosen can be varied to meet the desireddesign goals. Two possible relay choices are shown for both 120V and240V operation. The limiting factor is the flight time of the relaysbeing below the maximum design limit, (for example 14 milliseconds) toachieve the desired function. The board has both electrical controlconnectors for the control of the relays and to provide for reporting ofthe power characteristics as measured by the optional currenttransformer 2503 or other measuring circuits or devices located on theboard and power conductor connectors 2504. The board is assembled into abase relay module 2505, which has a housing 2506. A number of base relaymodules (5 in the present example) are then assembled via a powerconductor assembly 2507 into a another sub-assembly 2508 which iscompleted via the addition of a module relay driver and fault scanningboard 2509 which connects to each of the individual power modules viaits electrical control connectors and then has its own set of electricalcontrol connectors to connect to the ATS baseboard 2510 via an edgeconnector 2511. The power connectors of the sub-assembly 2508 are thenjoined via the power conductor assembly 2507 to connectors 2513 toattach to the ATS baseboard 2510. The completed sub-assembly resides ina housing 2515. The sub-assembly is then placed on the ATS baseboard2510 which has matching connectors for power 2513 and control/monitoring2511. The ATS baseboard can be designed with power andcontrol/monitoring connectors that allow for each sub-assembly to behot-swapped in the case of a fault, as discussed earlier. It should benoted that if the ATS was to incorporate the hot-swap feature, that themethod used to allow this is essentially an N+1 method (althoughdepending on the inrush current rating vs. steady state current ratingdesired, a N+2, N+3, . . . , N+Y method might be specified) where thereis always one or more sub-assemblies that are redundant and can be usedwhen another sub-assembly fails and needs to be taken out of service andthen replaced. This also allows the ATS design to advantageouslytolerate the higher inrush currents upon startup that are typical ofdata center power distribution. It can use the redundancy modules duringinrush startup and then take them out of service once steady-statecurrent is established. It should also be noted that fault-tolerance canbe implemented at a different level of the ATS. Each base relay modulecan incorporate redundant spare relays that can be used to replacedefective (or out of specification) relays at the point in time that anindividual relay fails. The failed relay can be marked as defective/outof service and a redundant relay in the base relay module can take it'splace. An advantage of this form of fault-tolerance is that it candeliver a longer mean-time-between-repair functionality, which is anadvantage in many operational environments. It should also be noted thatthe redundant relays can be used in a similar fashion as was describedfor redundant sub-assemblies earlier, to provide additional currentcapacity for inrush, as can happen during a cold start scenario or othercircumstances.

The ATS baseboard 2510 has connectors 2517 for the ATS control logicmodule 2516 which can incorporate the fault-tolerant scanning option.The fault scanning option monitors the function and health of eachindividual base relay module (including each single relay), eachsub-assembly and the system as a whole. If a fault is found, thesub-assembly containing the fault can be taken out of service, and itsfunction taken over by a redundant sub-assembly. The fault is reportedvia the communication module and the defective component can then bereplaced without taking the ATS out of service. The control logic modulefunctions can also be implemented redundantly, monitored forfunctionality and health and the modules made hot-swappable. The controlmodules can also add additional control redundancy features for improvedATS reliability which is discussed below. The control modules also canincorporate a communications interface for remote command, control andmonitoring of the ATS unit. FIG. 24 illustrates the power capacity ofeach sub-unit of the modular ATS and how they are combined from the basebuilding block of a 8 A-240V relay step-by-step all the way into a 2000A-240V modular ATS unit. Much larger capacities can be built using themodular parallel ATS methodology as desired and needed.

Other packaging methods can be used to provide additional flexibility indesigning modular ATS units in other form factors at other cost points,with or without current monitoring and fault-monitoring and redundancyfeatures as discussed earlier. This is illustrated in FIG. 24. In thisexample, the base relay modules 2401 are assembled via a controlconnector board 2402 and power busbar connectors 2403 into asub-assembly. The base relay modules and power connectors can be thesame components as used in the example ATS in FIG. 24, which leads tocost efficiencies across the product line family. The sub-assembly 2404uses a power access connector 2405 to connect the power busbarconnectors to the wiring harness of the ATS unit. The control module2406 is contained in a housing with an electrical connector 2407 for therelay control and optional monitoring/fault-tolerance functions. Thecontrol module then connects to the power sub-assembly via a suitablecable 2408. It can be implemented redundantly if desired either by usingredundant control modules housed in separate housings (this variant isnot shown on the drawing, but note the there is always a connectoravailable 2409 for a second control module to plug in) or incorporatingredundant control modules in the same housing. These design choices canbe selected to meet the desired cost, functionality and reliabilitygoals for each particular product. FIG. 26 shows how multiplesub-assemblies can be combined in different geometric arrangements toachieve modular ATS units of increased capacity that are suitable forenclosures of different shapes and sizes. They also demonstrate how amodular ATS that is designed to work with polyphase power inputs caneasily be constructed from the same building blocks, the only differenceis in the control logic synchronization needed to handle each powerphase which is discussed below. For example, A-B polyphase inputs(source A—phases X,Y,Z and source B—phases X,Y,Z) could each beappropriately wired to six base assembly 2601 units used to constructthe modular ATS units 2602 and 2604 shown in FIG. 26.

The flexibility in packaging of the modular parallel ATS can be used togreat advantage in a variety of situations. As an example, thesub-assembly units 2508 can be redesigned to connect into a structurethat is very similar to a modem panelboard and which can use the same orsimilar building blocks, such as busbars, cutout panels, enclosures,etc. that are used to make existing electrical panelboards, and have thegreat advantage of being mass-produced and already certified bycompliance organizations (for example Underwriters Laboratories) to coderequirements, (for example the National Electrical Code.) Thesub-assembly units could use the same exact types of busbar connectionlugs that current circuit breakers use in panelboards. They couldtherefore easily retain the ability to be hot-swappable. They could beused to create a modular parallel ATS that has adjustable currentcapacity, just add sub-assembly modules as needed to grow the capacityof the ATS! This could be used as a method to lower the price of a basemodel of the modular parallel ATS which has the ability to grow incapacity. This feature could be incorporated in any suitable model ofthe modular parallel ATS family that has the hot-swap option. Thecontrol connectors and control logic boards could be adapted to fit instandard-sized panelboard enclosures. The use of existing, approvedelectrical components such as used in panelboards and related productscould make the production of a variety of the modular, parallel ATSpotentially more cost effective and quicker to market. Any othermonitoring and management capabilities that are currently offered byanother vendor could co-reside in the enclosure on a separate logicdevice and easily be interfaced to the modular, parallel ATS controllogic unit, and offer enhanced functionality to the product offering.

It should be noted that the modular parallel ATS technology offers theability to design a cost-effective unit to desired Mean Time BetweenFailure (MTBF) and Mean Time To Repair (MTTR) target values. This isbecause the level of redundancy in the design can be adjusted as neededat several points:

-   -   At the Base Relay Module level—The number of redundant relays on        each base relay module can be changed as needed to offer the        required redundancy.    -   At the Sub-Assembly level—The number of hot-swappable        sub-assembly units can be changed as needed to offer the        required redundancy.    -   At the Control Module level—The number of hot-swappable control        modules can be changed as needed to offer the required        redundancy (with self-health reporting two modules should be        sufficient, but more could be added if desired).

This ability to cost-effectively design to needed MTBF and MTTR levelsallows the consideration of other power distribution topology options.Also, the failure mode of the modular parallel ATS unit is differentfrom traditional ATS units. There is really no single component in theunit that can fail and take down the whole ATS. This is an importantdifference and the ability to design to reliability and repair targetscombined with the difference in failure modes enables the use of themodular parallel ATS in a number of ways that do not suffer from thedisadvantages of traditional ATS units.

As noted earlier, a single traditional ATS unit with an MTBF of 200,000hours is much less reliable than a group of ATS units at the lowerlevels of the power distribution topology (branch, leaf, see FIG. 1 forthese definitions). However, if desired and useful, a modular parallelATS device with sufficiently high MTBF and MTTR values could beconstructed using the methods described herein to use in switching athigher levels of the power distribution topology (root and coreinfrastructure, see FIG. 1 for these definitions). The MTBF and MTTRtargets would need to be quite high, but the modular parallel ATS couldbe used to hit them. This usage of the modular parallel ATS isinnovative because it essentially eliminates the downside of using ATSswitching due to how it handles sub-component failures and because itoffers the benefits of reduced cost, sufficiently fast switching timesfor EDP equipment and greater efficiency than the solid-state ATS unitsthat are currently used in this role.

The flexibility that the modular parallel ATS methodology provides isvery useful. It allows for the construction of ATS units in form-factorsand capacities that are very useful in data center power distribution.Two examples are shown in FIG. 27. Both are units that can be connectedto end-user equipment via receptacles or receptacles feeding hydra cordsor hydra-cords that are hardwired into the ATS units (not shown). Thelatter option is a cost-effective method for building an in or near rackpower distribution system that is auto-switched and has the length andgauge of each element of the hydra cords optimized to feed power to each1 U (or other modulus) of the rack with the least amount of powerwiring. This promotes efficient cooling airflow by minimizing excesspower cabling. It is especially useful for large-scale computingenvironments (Google, Ebay, etc.) where the configuration of the EDPequipment placed in the rack is designed and known in advance and therack with EDP equipment is placed in service as a unit and replaced asunit at the end of its service life. Another useful form-factor is amodular ATS that is designed to be located in the rack to minimize itsusage of rack space in conjunction with the EDP equipment it ispowering. An example would be a EDP end-user device that has four powersupplies in an N+1 configuration. Such a device cannot be redundantlyconnected to two A-B power sources, because it requires three of thepower supplies running to function. A solution is to auto-switch the A-Bpower sources to each power supply. Such a device is usually reasonablylarge and occupies multiple 1 U spaces in the rack. An auto-switch thatis optimized to work with such a unit might optimally use an enclosurethat allows the auto-switch to be co-located with the EDP unit, byresiding behind it, but in the same set of 1 U spaces in the rack. Inthis case, the ATS enclosure would be shaped to best work with the EDPequipment and provide the needed airflow paths, such that the EDPequipment could properly cool itself. The modular ATS could also beintegrated into the enclosure of the EDP equipment itself. The modularATS methodology makes it much easier to adapt to such a form-factorrequirement. It should also be noted that such a use of an ATS is novel,it allows for the use of fewer power supplies (and each power supply hasa minimum loss factor, so using less power supplies is more efficient)if the power supplies that are available to a EDP manufacturer are ofsuch size and capacity that the EDP unit needs to run on an odd (ratherthan even) number of power supplies (excluding 1). In this case the EDPunit can be designed be redundant on A-B power by incorporatingauto-switching of the power sources.

FIG. 28 shows an example functional block diagram of the control logicof a modular ATS constructed in accordance with the present invention.The control arrangement shown is for single-phase power, but can easilybe adapted to polyphase power as is described below. FIG. 29 shows anexample functional block diagram of the control logic which adds anoptional communications controller and an optional fault-tolerancemodule. The fault-tolerance module monitors the status and condition ofthe basic relay modules and the sub-assemblies that contain them asdescribed earlier. It also controls the disabling of any failedsub-assemblies and the substitution of a redundant sub-assembly in theirplace. FIG. 30 shows an example functional block diagram of the controllogic which adds an optional control redundancy feature. In this variantthe control logic is replicated into three different sub-sections andthe output of each sub-section is compared so that if one has an errorits result is overridden by the results of the other two. This type oflogic control is called “majority voting” or “tell me three-times” andwas most famously instituted in the hat-box spaceflight computerdesigned for the Apollo program. It is still commonly used in thecontrol logic of spacecraft, due to its resistance to computationalerrors caused by gamma and other radiation types found outside of theEarth's atmosphere. The reason that the modular ATS might wish to usethis type of logic is its extremely high MTBF ratings and resistance tofalse logic outputs. An ATS built with this type of logic will almostnever have a logic failure. The most common points of failure in an ATSare relay, logic and logic power supply. The modular parallel ATS designdescribed makes all of these redundant, fault-tolerant, monitorable andhot-swappable. The net result is an ATS that will probably run withnearly indefinite uptime given proper maintenance, meeting the demandsof the modern data center.

The example control logic designs presented can be implemented asanalog, digital or hybrid (mixed analog and digital design). The digitallogic can be implemented in discrete digital methods or other methods,such as PAL's, FPGA's etc. The choice of method will be dictated byavailable components, cost-constraints and other design criteria, suchas making an implementation that is difficult to reverse engineer andcopy.

FIG. 31 displays an illustrative example of an electrical currentsharing design constructed in accordance with the present invention. Ina parallel array, or sets of relays, (a set having one or more relays)where the electrical current design capacity is the sum of the capacityof the individual relays, a key design issue that must be solved is howto properly manage current flows across all of the relays to insure thatnone of them prematurely fail. This is especially important duringcurrent inrush and when switching occurs, since not every relay willhave the exact same resistance and transfer time.

The consideration is that when numerous sets of relays are connected inparallel in an array, that current sharing among those relays should bemaintained so no one relay, or combination of relays is unbalanced.Otherwise, one or more relays could be subjected to more than its ratedcapacity. This can cause the relay to fail and/or shorten its normaloperational lifetime. If the current sharing is not sufficientlyuniform, the relays carrying the excess current will likely fail,causing a cascade of failures. To prevent this, some method should beused to guarantee current sharing. This section describes design optionsto deal with this issue as they apply to the modular parallel ATS.

There are two states where the electrical current must be balancedacross the sets of parallel relays. The states are: 1) Constant currentflow; 2) When the sets of parallel relays are opening or closing, asoccurs when the parallel ATS is switching.

The problem of insuring balanced current flows in the both of thesestates is related but each has some different considerations. In theconstant current state, the primary issue is managing resistance acrossthe sets of parallel relays, to insure that the capacity limits of eachindividual relay is not exceeded and the overall efficiency andreliability of the parallel ATS is optimized. The variance in resistanceacross sets of parallel relays is caused by small variations in theoperational characteristics of production relays, which are usuallyconsidered within normal production batch tolerances. It also can be aresult of production tolerance variations in the fabrication andproduction of the parallel ATS.

When the sets of parallel relays are opened or closed, due to smallvariations in the operational characteristics of production relays,which are within normal production batch tolerances, the relays will notopen or close with the exact same timing. This is called relay skew.Relay skew can also be caused as a result of production tolerances inthe fabrication and production of the parallel ATS. There are a numberof ways to deal with the issue of relay skew in the design of a parallelATS.

-   -   1. Relay pre-production selection—This method pre-tests batches        of relays to insure that they are all close enough to a        specified set of operational tolerances to work in the parallel        ATS application.    -   2. Relay timing compensation—This method varies the timing of        the control signals sent to actuate each relay so that the        variation in the actuation time of each relay is compensated for        and the sets of parallel relays operate with relay skew reduced        to the desired values. The actuation time of each relay (and/or        sets of relays) can be measured and stored as a digital value as        part of the production process of the parallel ATS and can be        measured and updated in real time each time the parallel ATS        switches, which offers the ability to adjust the control signal        timing over the life of the relay and to monitor the health of        the relay and notify when the relay (or the module it is part        of) should be taken out of service and/or replaced.    -   3. Current limiting/diverting—The sets of parallel relays will        all open or close in a relatively short time interval if they        are selected to have sufficiently tight operational tolerances.        However, regardless of how closely matched the relay timing is        with respect to each other, there will be some period of time        that differentiates each relay. This means that another approach        to preventing damage to sets of parallel relays is to limit (or        delay) the electrical current that is applied to them in certain        critical time periods (for example when the relay(s) are just        opening (or when they are just closing) and could be damaged by        having currents in excess of their rated capacity applied. This        can be done by one of three methods.        -   a. Resistance—If sufficient in-path resistance can be            applied during the critical time period, then the current            can be limited and the sets of parallel relays will not be            damaged. The resistance can applied via a number of methods,            for example resistors, negative temperature coefficient            (NTC) power thermistors, etc., either on the inputs, outputs            or selected points in the power paths of the parallel ATS.        -   b. Inductance—Inductors can be used to limit the rate of            change of transient electrical energy for a short period of            time, limiting current values across the sets of parallel            relays during critical times.        -   c. Diversion—Fast acting semiconductor switches (for example            triacs) can be used to divert the current path around the            sets of parallel relays when needed, for example during the            critical time period while closing. This technique also has            the advantage that the transfer time of the parallel relay            sets (and therefore the parallel ATS) become programmable            with the lower limit being the switching time of the            semiconductor switching device, which is measured in            sub-microseconds.

Variations of the modular parallel ATS can use any or all of thesetechniques in any combination to produce an effective solution to theproblems of current load balancing (including relay skew). Somepreferred instantiations of solutions are described in more detailbelow.

1) Constant Current Load Sharing.

In a traditional parallel relay, or switch of any type, a smallresistance is placed in the output of each relay stage that will helpbalance the loads among the array. This is general practice. It works ifa small loss of power is acceptable. This is method would work, but isnot an optimal solution for the modular parallel ATS, because it wastespower.

In the modular parallel ATS, load sharing is accomplished byincorporating that small resistance as part of the power delivery path.Simply put, the resistance of the relay contacts, plus the leads used toattach the individual relays to the input and output buss providesufficient resistance to balance the high volume, high consistencyrelays planned to be used in production units. As in all cases ofmanufacturing, there are a certain number of units that will fall out ofthe “normal” range of expected variations in tolerances. These deviceswill inevitably have the characteristics of either passing too much ofthe load for their cell (lower than nominal resistance) or not passingtheir share of current (higher than expected resistance). In either ofthese cases, the problem can be solved by supplying a percentage ofredundant spare relays in the array to handle the current of thedefective relay, and simply not turning on the defective relay. Thisrequires that there be monitoring of all the relays in the array. We cando this with a current sense transformer on every cell as part of themodular array. A faulty relay is decommissioned after it is determinedit is no longer usable, and an alert set by the controller to indicatethe faulty module should be replaced. The design of the modular systemallows for “hot swapping”, or the changing of the failed componentswhile the remainder of the array is functioning as was discussedearlier.

2) Current Sharing at the Time of Closing or Opening of an IndividualRelay.

When an array of (or sets of) relays are connected in parallel, due tomechanical variations, some of the contacts will either connect ordisconnect before or after others. A distribution of times is inherentin mechanical components. Even very well made mechanical components willhave different event durations. These variations may be on the order ofonly a few microseconds, or as much as a millisecond or so. In anyevent, at some level of time, one relay out of the entire array willmake contact first, and one will break contact first. Then another, thenanother, and so on until all have made the transition. As far aselectricity is concerned, the time from the first to the second relaytransition is functionally irrelevant. The first relay to make contactwill carry all of the current available until another is there to shareit. On massively parallel arrays connected to very low impedances at thesource and the load sides, the currents will go high enough to damageindividual relays, even if the current is present for only a fewmicroseconds. If the damage is not immediate, it will likely beaccumulative. In any case, a means to control excessive current fromdamaging individual relays must be employed to achieve desiredreliability and service lifetime goals.

This is accomplished by adding an innovative form of inrush control,different from how it is presently commonly practiced. The basic conceptof inrush control is well established and has specific electroniccomponents designed and produced for exactly that purpose. Thecomponents are referred to as Negative Temperature Coefficient (NTC)resistors. They are sometimes called thermistors, or inrush limiters,but all have one characteristic in common, as the temperature rises, theresistance lowers. Since the resistance is relatively high in thesedevices when they are “cold” (typically room temperature) they providesignificant balancing resistance, and overall current limiting in acircuit when they are first turned on. In the example of the HighVoltage Micro ATS, it operates on 240 VAC. The relays in that device,which are the same relays that could be used in the base power module ofthe modular parallel ATS are capable of handling up to 50 amps for atleast two or three AC cycles (32 to 48 ms.) with no degradation. Thus ifcurrent is limited to that amount, for the time period above, the relayswill sustain no damage. Thus, if an NTC resistor is placed in serieswith the relay contacts, and that resistor has a (for example) “cold”resistance of 5 ohms, then when power is applied, the greatest possiblecurrent is 240V/5 ohms (ohms law) for a maximum of 48 amps. This is acurrent level that the contacts can handle until other relays in theparallel array can finish closing and share the load which then reducesthe current in the relay back down to the acceptable continuous load forthe contacts. Since all of the relays in the array will have a maximumtotal variation, then the limiting NTC resistor is only needed for thattime. All the rest of the time it would normally be dissipating power.After power is applied to a NTC device, its internal resistance,combined with the current through it cause it to self heat. Since theresistance goes down with temperature, as the temp of the resistorincreases, the resistance goes down, and at some point it reaches anequilibrium of current and voltage drop. In the case of the zATS and themodular base power arrays for the parallel modular ATS, this point isaround 0.03 ohms. But even at that, the NTC resistor must maintain selfheating, and thus, would consume about 3 watts of dissipation at themaximum load of 10 Amps for a given relay. This is not much, but whenmultiplied by the 400 relays associated with a large 4000 Amp matrix, itwould add up to 1200 W of heat dissipation. This is nearing the loss ofa very well designed Solid State Switch, or the so-called Static Switch.

A key point of the Zonit array is power efficiency, so we have devised away to limit this loss factor. Only a couple of milliseconds is the timeperiod while the NTC resistor needs to be active. So, we have added anadditional relay attached in parallel to the NTC resistor. It iscontrolled by the circuits in the modular parallel ATS controller to beopen during a transition event, and be closed when in continuousoperation. In this way, the NTC resistor is “bypassed” by a very lowimpedance set of contacts in the auxiliary relay, thus nearlyeliminating the heat dissipation losses of the traditional means.

It should be noted that due to the short time period when the thermistoris not bypassed and is carrying the current, it may be possible to use aless expensive resistor instead of a thermistor. It should also be notedthat the varistor 2502 shown on FIG. 25 is used to prevent damage to theindividual relays from voltage spikes resulting from power qualityevents. The varistor protection function can be integrated into eachbase relay module as shown or could be integrated as a separate set ofcomponents into each subassembly 2508 (not shown in FIG. 25, or designedas a separate sub-module (this approach takes advantage of existingcomponents that are already available in the market) inside of the sameenclosure or external to it that is installed between the modularparallel ATS and the power source.

Turning now to FIG. 31, the three configurations mentioned above areoutlined in the schematic representations of a five relay module of alarge matrix in the top of the drawing. At the left is a standardparallel relay configuration that is subject to contact degradation. Themiddle drawing shows the addition of the NTC Current Limiting resistors,as would be used in a traditional solution for contact load sharing andinrush control. On the right is the Zonit modified version with anadditional set of relay contacts in parallel with the NTC resistor, asdescribed above. In drawing subsets 1 through 8, the steps associatedwith controlling the main relay and the bypass relays are described forboth the case of the period just before closure through a short timeafterwards, and just prior to the opening of the relays, to the timewhen the whole process can start over.

Sequence of events for switch closure:

-   -   1. Relay is open, just prior to closing, no current flowing.    -   2. Primary relay closes, NTC resistor bypass relay is open.        Current starts to flow between source and load. Assuming this is        the first relay in the array to close, all of the available        current flows towards the low impedance load. It is assumed that        the load is capable of being many times the amperage rating of        the described relay. At this time, just after current starts to        flow, the NTC resistor bypass relay is open and current is        passing through the NTC resistor. It is cold and is at 5 ohms.        Even if the load is close to zero ohms, the current passed        through this one primary relay is limited to about 48 amps.    -   3. During the time frame from step 2 to step 3, all of the        relays in the parallel array have closed. In reality, this will        generally all happen within about 1 millisecond, but        nonetheless, by 12 to 15 milliseconds, the complete array is on        and all cells are in parallel. The NTC is heating up but still        not completely hot. It is perhaps down to a resistance of 3 or 4        ohms by now, but on the way to fully hot. Loads are shared        between relays in the array and resistance is still fairly high        in the NTC resistors. The mass of the resistors must be heated        up, this takes several hundred milliseconds, even seconds,        depending on the device selected. As long as the device selected        can meet the need for the first 17 milliseconds, additional        capacity is not required. At 17 milliseconds the final event        occurs.    -   4. T+17 ms., and the bypass relay closes, shorting out the NTC        resistor. The contact resistance of the relay is about 0.002        ohms, so it now carries the vast majority of the current. But in        addition, for added durability, the closure of the bypass relay        is done exactly at the time the current is passing through zero,        as is done in the μATS and the modular ATS controller during        transfers from B to A. Thus, at the time of the relay closure        and bounce period, minimal current is present, even on a fully        loaded array. The power path remains in this state until        disconnection, and total power dissipation is reduced to less        than a half watt across all of the contacts in the relay array.        This is orders of magnitude better than the best solid state        switch, or “Static Switch”.

Sequence of events for switch opening:

-   -   1. On the bottom row of panels in FIG. 31, the sequence of        operations for opening the modular parallel ATS are described in        panels 5 through 8. Disconnection of relays has the same        distribution of timing across an array of relays, just as the        closure time of the array of relays does. Thus, containment of        sequentially building currents up to the last relay to        disconnect must also be considered. Panel 5 shows the same state        as pane 4, the continuous running state, just prior to the        disconnect event.    -   2. Frame 6 shows the time just before zero crossing of the        current, and the bypass relay being opened. In an ideal world        this would coincide with the opening of the primary relay, but        the NTC resistor bypass relays have the same distribution of        timing as all the other relays do, so it must be opened just        prior to the opening of the primary relay to insure that all of        the bypass relays in the matrix are open before opening even the        first primary relay. Since this is done at approaching zero        crossing, little heating of the NTC resistors occurs, as little        current flows at this time.    -   3. Frame 7 shows the state when the primary relay has just        opened. Assuming all of the other relays have opened by this        time also, the last relay to open was carrying the maximum load,        but that was limited by the NTC resistor to less than 50 amps,        and for less than 6 ms.    -   4. Frame 8 shows the cool-down time for the NTC resistor. Since        the μATS based modular parallel ATS controller has a minimum 3        second delay between return of A side power, and connection to        the A side after it is stable, the NTC resistors are guaranteed        the time required to cool to a “reset” state.

Flexible Power Topologies and Operational Modes based on the ModularParallel ATS The availability of multiple parallel power paths in themodular parallel ATS offers unique flexibility in how it can be used indata center and other environments where fast switching ATS capabilitiesare needed. Normally there are two input and one (“Y” topology ATS) ortwo (“H” topology ATS) outputs for traditional Automatic TransferSwitches. The modular parallel ATS can function as multiple discrete ATSunits in (either the “Y” or “H” style ATS topology) the same unified andspace-efficient form factor, that are all controlled by a unifiedcontrol logic that is programmable. The modular parallel ATS can havemultiple parallel inputs ((A1, B1), (A2, B2) . . . ) and multipleparallel outputs (C1, C2, . . . or C1, D1, C2, D2 . . . ) (depending onwhether the ATS is configured in “Y” or “H” ATS topologies). The uniqueaspect of the parallel modular ATS is that it can be connected to thesemultiple inputs and outputs as needed and desired as long as the powerhandling capacities of the parallel power paths are respected. Forexample it is possible to configure the modular parallel ATS to outputto multiple separate output branch circuits. Each output could feed aseparate panel or a busbar, for example. The modular parallel ATS couldbe controlled to set which source, A or B, each output branch circuitwas being fed by and/or preferred as a source. It also could becontrolled to switch in either a “Y” topology (two inputs, one output)or an “H” topology (two inputs, two outputs). FIG. 33 shows an exampleconfiguration that demonstrates the flexibility of the parallel modularATS. The topology shown could use the utility grid 1805 as the A1 to theATS 1840 a. The UPS 1835 could be the B1 input and the UPS 1836 could bethe B2 input. The outputs could be to the main panelboards, 1835, 1836.This capability allows the data center manager to select conditions andpreferences that decide when and how to make one or more transfers(which source to use for each separate output, conditions (load, powerquality, other) that trigger a transfer for some or all inputs and/oroutputs, etc.) that can be useful for operating and maintaining thefacility. The percentage of total load on each A-B source pair can becontrolled, for example. Another possibility is programmable intelligentload shedding. The parallel modular ATS can disconnect a selected outputinstead of just switching it between input sources. This means that eachindividual output can be selectively and reliably disconnected, avaluable feature. It is desirable to put as few points of failure in thepower distribution path in a data center as possible. The ability todisconnect as well as transfer in a highly reliable ATS is useful. Itoffers the data center manager a much richer set of power distributionoptions: multiple topologies, control options and possibilities.Traditional ATS units cannot deliver this range of capabilities.

Increased Efficiency for Traditional Power Distribution Via UPS LoadShifting

As discussed earlier, it is normal practice to share loads when two A-BUPS units are used in a data center as the power sources. This isusually due to the nature of the end use equipment having dual powersupplies that distribute the load more or less equally to both the A andB power supply inputs. Also, as earlier covered, this reduces UPSefficiency since they must not be loaded over 50% to function in aredundant power configuration. Using large numbers of μATS™ switches itis possible to raise the efficiency of such a power distribution systemas follows. All of the electrical load for EDP equipment in the datacenter can be “Load Shifted” via μATS™ units onto one of the two UPSunits, increasing the efficiency of that UPS unit as shown in the UPSefficiency curve shown in FIG. 3. The other UPS unit is at idle and willonly be used if the primary unit fails. The UPS units must be designedto handle this type of load being immediately placed on them, but almostall modern UPS units can do this. The result is an increase of ˜3-5% inthe efficiency of the data center, a useful improvement. It should benoted that while only one pair of UPS units is discussed here themethodology scales to larger data centers that have many UPS unitsdeployed in pairs for redundancy.

The methodology to accomplish this is simple and can be deployedincrementally for each piece of EDP equipment, reducing service impacts.Every single power supply (or corded) EDP device will be connected via aμATS™ to the A and B UPS units. Every dual or N+1 power supply EDPdevice will have one power supply connected to the A UPS via a normalpower cord, the second or all other N+1 power supplies will be connectedto the A and B UPS units via μATS™ units.

This insures that when the A UPS unit is available it takes all of theload and when it is not the B UPS carries the load. The μATS™ units canbe deployed in one to one per device ratios, or low integer numberratios, respecting μATS™ power capacity limits.

Almost all EDP devices share the load among all available power suppliesin the device. It is possible to build an EDP device that switches theload between power supplies, so that only one or more are the activesupplies and the others are idle, but as described earlier, this israrely done for both cost and reliability reasons. To insure thatmulti-power supply EDP devices draw on only filtered utility line powerif it is available and switch to the UPS if it is not, each of thesecondary power supply units needs to be auto-switched between theutility line and UPS unit(s). Otherwise, the UPS unit will bear aportion of the data center load, lowering the overall efficiency of thepower distribution, which is undesirable.

ATS Design with suitable characteristics for Highly Parallel PowerDistribution Traditional ATSs tend to have limitations that preventtheir effective use in implementations of highly parallel,auto-switched, power distribution architectures. For example, thesetraditional ATSs may typically be too inefficient, consume too much rackspace, and cost too much. Embodiments of the micro-ATS described hereinaddress some or all of these issues.

According to one embodiment, the micro-ATS (e.g., the Zonit μATS™) isvery small (e.g., 4.25-inches×1.6-inches×1-inch, or less than 10 cubicinches) and very efficient (e.g., less than 0.2 volts at maximum loadloss). Certain implementations use no rack space, as they areself-mounted on the back of each EDP device, incorporated in thestructure of the rack outside the volume of the rack used to mount EDPequipment, incorporated in rack-mounted plugstrips, or incorporated inan in-rack or near-rack Power Distribution Unit (i.e., any of whichbeing possible due to the small form-factor of the micro-ATS). In otherimplementations, the micro-ATS is small enough to be integrated directlyinto the EDP equipment itself.

Various embodiments of micro-ATSs are described herein, including theirvarious components. For the sake of clarity and context, the micro-ATSembodiments are described as switching between two separate powersources, “A” and “B.” In some implementations, the A and B power sourcesare single-phase sources. In other implementations, polyphase powersources are connected. Where polyphase power sources are connected,polyphase embodiments of micro-ATSs are used. Substantially the samecomponents (e.g., circuits) described herein with reference to thesingle-phase implementations are applicable to the polyphaseimplementations.

For example, polyphase embodiments can be implemented as multiplesingle-phase micro-ATS units acting in parallel, with additionalfunctionality provided for synchronizing certain of the control circuitsso that they act together across the multiple ATS units to handleswitching and return from one polyphase source to the other polyphasesource and back. Various embodiments of polyphase micro-ATSs can alsohave different conditions under which to switch power sources. Forexample, given three phase power with X, Y, and Z “hot” leads, a faulton any of three might be considered reason to switch from the A to the Bpolyphase source. To return to the A polyphase source, it may bedesirable to ensure first that all three hot leads are present, stable,and of sufficient power quality on the A source.

Various ATS implementations and associated system architectures will nowbe described. Turning first to FIG. 7, a system diagram of anillustrative micro-ATS 700 is shown, according to various embodiments.As illustrated, the micro-ATS 700 is connected to an “A” power source760 and a “B” power source 765, and uses its various components toprovide output power 770 to one or more devices or distributiontopologies (e.g., to one or more EDP devices in a branch circuit of adata center). The micro-ATS 700 includes a power supply subsystem 705,an “A” power voltage range detect subsystem 710, an “A” power lossdetect subsystem 715, a “B” power synchronization detection subsystem720, an “A”/“B” synchronization integrator subsystem 725, a timingcontrol subsystem 730, an “A” & “B” power switching subsystem 735, anoutput current detect subsystem 740, a disconnect switch subsystem 745,and a piezoelectric device driver subsystem 750. Embodiments of thepower supply subsystem 705 include innovative ways of powering controlcircuitry of the micro-ATS 700. Embodiments of the “A” power voltagerange detect subsystem 710 determine if the power being supplied to themicro-ATS 700 is in a desired (e.g., predetermined) voltage range.Embodiments of the “A” power loss detect subsystem 715 determine whenthe “A” power being supplied to the micro-ATS 700 has been lost usingdesired discrimination characteristics. Embodiments of the “B” powersynchronization detection subsystem 720 measure the timing of thealternating current waveform of the “B” power. Embodiments of the“A”/“B” synchronization integrator subsystem 725 provide synchronizationof “B” to “A” transfers at zero voltage crossing times and “A” to “B”integration functionality. Embodiments of the timing control subsystem730 control when the selected power source to the micro-ATS 700 isswitched, either the “A” source to the “B” source or from the “B” sourceto the “A” source, and can handle over-current condition switching andrelay sequencing. Embodiments of the “A” & “B” power switching subsystem735 control actual switching between the “A” and “B” power sources ineither direction to change which supply is acting as the input powersource to the micro-ATS 700.

Embodiments of the output current detect subsystem 740 detect andmeasure presence and various characteristics of output current from themicro-ATS 700, and can, in some embodiment, mimic characteristics of afuse so that the micro-ATS 700 can protect itself without blowing actualphysical fuses (i.e., which must be replaced). Embodiments of thedisconnect switch subsystem 745 disconnect a secondary power source fromthe power supply when it is not in use. Embodiments of the piezoelectricdevice driver subsystem 750 implement innovative techniques for drivingpiezoelectric or other devices.

Each component is described below as performing particular functionalityin the context of the micro-ATS 700. It will be appreciated that otherconfigurations are possible in which similar or identical functionalitycan be implemented using other components, combinations of components,etc. Further, in some cases, values are given for components such asresistors and capacitors, etc. and ranges are given for current,voltage, and/or other power characteristics. These values and ranges areintended to add clarity to illustrative examples and should not beconstrued as limiting the scope of embodiments.

FIG. 8A shows a circuit diagram 800 of an illustrative power supplysubsystem 705 a in context of an illustrative “A” & “B” power switchingsubsystem 735 for use in some embodiments of a micro-ATS 700. Asdiscussed above, the micro-ATS 700 is connected to an “A” power source760 and a “B” power source 765. The power supply subsystem 705 aperforms a number of functions, including power conditioning (e.g.,current limiting and power clean-up).

The source power for the power supply subsystem 705 a is acquired fromthe center taps of RY3 H (“Hot”) and RY1 N (“Neutral”). Thus, the sourceof power for the ATS Power Supply is from the “A” side when the outputof the micro-ATS 700 is on the “A” Side, and on the “B” Side whentransferred to the “B” side. Components of the “A” & “B” power switchingsubsystem 735 serve as the automatic transfer switch for the micro-ATS700 power supply subsystem 705 a. The current available from outputpower is limited by R3. ZD10 limits the full wave rectified output ofthe bridge BR4 to 150V peak. ZD10 guarantees that C1 does not exceed itsrated voltage. C1 stores enough charge to allow HV (“High Voltage”)operations of the relays during transitions between the “A” power source760 and the “B” power source 765.

During an over-current fault, neither the “A” power source 760 nor the“B” power source 765 is available at the output power 770 node, but RY2and all the rest of the micro-ATS 700 circuitry may still need power.This is accomplished by node A2 775 which manifests “A” power 760 at theNO terminal of RY2 via C16 and BR6 when RY2 is activated. C16 limits thecurrent available during a fault.

Bridge BR6 normally blocks A2, as will be discussed more fully below.When a fault occurs, GC On will be pulled almost down to Common, andpositive power will be available at U5 LED via ZD11. This turns on theU5 transistor. The U5 transistor and Q3 form a Darlington pair thatshorts the bridge BR6, allowing A2 to drive HV through diode D9. A2 alsodrives LV (“Low Voltage”) through diode D10. C20 provides filtering andstorage for LV.

In some embodiments, as illustrated in FIG. 8B, the 15-volt power supplyis normally supplied by HV through R63, R64 and R65. These threeresistors drop the voltage and limit the current for Zener diode ZD2.ZD2 regulates the voltage for the comparator and other electronics onthe control board. C17 further filters out the 15-volt signal. During afault condition A2 provides power for the 15V supply through LV. HV ispulled down to 45V in this condition due to current limiting capacitorC16 mentioned earlier.

Embodiments of the power supply subsystem 705, such as the embodimentsillustrated and described with reference to FIGS. 8A and 8B, provide anumber of innovative features. One such feature is that some embodimentsof the power supply subsystem 705 acts as a transformer-less, veryhigh-efficiency power supply. For example, as illustrated above, thecircuit produces low and high-voltage DC power from multiple AC inputsthat is suitable for powering both low-voltage control circuitry andhigher power relays. It does so very efficiently and with a minimum ofexpensive analog parts.

Another such feature is that some embodiments of the power supplysubsystem 705 provide capacitor current limiting for very low-powerusage. As illustrated above, power consumption of the power supplysubsystem 705 is limited by use of a capacitor. This can efficientlylimit the power supply capacity to a desired value, thereby providingmaximum efficiency and low power consumption.

Yet another such feature is that some embodiments of the power supplysubsystem 705 provide optical isolation to reduce or even eliminatecross currents As will be discussed more fully below, embodiments of thecontrol and synchronization subsystems (e.g., the “B” powersynchronization detection subsystem 720, the “A”/“B” synchronizationintegrator subsystem 725, the timing control subsystem 730, etc.)optically isolate between input power sources, virtually eliminatingcross-currents between them.

Still another such feature is that some embodiments of the power supplysubsystem 705 provide power control relays (e.g., illustrated as RY1,RY2 and RY3) to direct the source power to the output of the micro-ATS700 as well as provide the internal source selection (transfer switchfunction) for powering the micro-ATS 700 power supply subsystem 705.

And another such feature is that some embodiments of the power supplysubsystem 705 use an optically isolated disconnect circuit to preventcross-source currents when the micro-ATS 700 is in the over-currentfault mode. In this mode, there is no power delivered to the output, andthus, power must still be delivered to the micro-ATS 700 control andrelay drive circuitry. As illustrated above, this can be accomplishedvia the A2 775 power path, and controlled by BR6 and optical isolationcontrol U5.

FIG. 9 shows a circuit diagram of an illustrative “A” power voltagerange detect subsystem 710 a for use in some embodiments of a micro-ATS700. Embodiments of the “A” power voltage range detect subsystem 710 areceive “A” power 760 nodes AH and AN. The “A” power 760 is full waverectified by bridge BR2. C3 is used to limit the current available inthis and the “A” power loss detect subsystem 715, as will be describedbelow. In normal operation the “A” power voltage range detect subsystem710 a can generate the A (ON), A (COM), and CQ18 signals to the “A”power loss detect subsystem 715.

The illustrated “A” power voltage range detect subsystem 710 a includesover-voltage detection and under-voltage detection functionality.According to the over-voltage detection functionality, D18 half-waverectifies the “A” power 760 and drives a ladder comprised of R14 andR27, which charges C4. When over-voltage occurs on “A” power 760, ZD6and Q36 will begin to conduct drawing current through resistors R7, R74,R6, R5, and R1. This will turn on Q34, which will pull up the voltage onC4 through R17. This will latch Q35, Q36, and Q34 in an on state. Thisalso will pull current through R8, thereby turning on the over-voltageindicator, LED2. C2 will be charged and ZD5 will conduct. Q32 and Q31will conduct, turning off Q37 and Q38. This turns off A (ON). In theillustrated embodiment, this will tend to occur at around 135 VAC at AH,though other over-voltage thresholds can be set as desired.

Under-voltage functionality detects when “A” power 760 is below adesired low-voltage threshold. As illustrated, increasing diode D18 willcharge capacitor C5 via the ladder formed by R16 and R30. When thecharge on C5 reaches a preset level (illustrated as 100 VAC, but otherlevels can be set as desired), ZD8 starts to conduct through R31 andR58. Q1 and Q2 will start to turn on, pulling current through R10, D12and R9. This turns on Q37 and Q38 applying power to A (ON). This in turndrives current through R35 and D11, which turns Q1 and Q2 on harder andadds hysteresis to the voltage on C5. If “A” power 760 is at normalvoltage and decreasing, the “A” voltage will have to drop to around 88VAC (or any other desired value) to turn A (ON) off. This is due to theadditional current through R35 and D11 charging C5 when A (ON) ispresent.

When the “A” power loss detect subsystem 715 is on, signal CQ18 will below. ZD9 and D1 will lower the voltage on the emitter of Q1. Q1 and Q2will be turned on harder serving to improve the hysteresis of the undervoltage circuit. C6 and R2 act to smooth out the A (ON) signal. C6provides storage so that the zero crossings of the rectified AC signaldo not turn the A detect circuit off. R2 controls the decay time of thedischarge of C6 when power is lost on the “A” power 760 side.

Embodiments of the “A” power voltage range detect subsystem 710, such asthe embodiments illustrated and described with reference to FIG. 9,provide a number of innovative features. One such feature is that someembodiments of the “A” power voltage range detect subsystem 710 providevery high efficiency. As illustrated, using high impedance componentsand switching off of the power delivery to the “A” power loss detectsubsystem 715 as the technique for initiating and holding the voltagefault conditions is very efficient and consumes a minimum amount ofpower. In addition, the “A” power voltage range detect subsystem 710also provides all power to the “A” power loss detect subsystem 715, andhas current limiting provided by C3. Use of a capacitor for currentlimiting minimizes power consumption by returning unused current to thesource on each half cycle instead of wasting it as heat as in atraditional resistor limiting technique.

Another such feature is that some embodiments of the “A” power voltagerange detect subsystem 710 provide easily programmed over-voltage detectdelay. As illustrated, the over-voltage detect functionality uses asingle capacitor value (C4) to determine the delay for detecting anover-voltage condition. Another such feature is that some embodiments ofthe “A” power voltage range detect subsystem 710 provide easilyprogrammed “A” voltage OK delay. The “A” power voltage range detectsubsystem 710 a determines whether the voltage from “A” power 760 is“OK.” That functionality uses a single capacitor value (C5) to determinethe delay for accepting the A input voltage for start-up of themicro-ATS 700, and can be easily adjusted for various requirements.

Yet another such feature is that some embodiments of the “A” powervoltage range detect subsystem 710 provide an easily programmedthresholds for “A” under-voltage detect, “A” voltage OK, and “A”over-voltage detect. Under voltage assumes that the voltage was at onepoint acceptable, and that it is now lower than desired. As illustrated,a single resistor value (R35) controls the difference between theacceptable value and the low voltage shut down point. Similarly, the “A”voltage OK threshold can be programmed via a single resistor valuechange (R16), and the “A” over-voltage threshold can be programmed via asingle resistor value change (R14).

FIG. 10A shows a circuit diagram of an illustrative “A” power lossdetect subsystem 715 a for use in some embodiments of a micro-ATS 700.Embodiments of the “A” power loss detect subsystem 715 handlefundamental operation of the primary power (“A” power 760) detect anddelay portions of the micro-ATS 700.

The simplified overview of the “A” side power sense and delay circuit isshown. A description of the fundamentals of a Silicone ControlledRectifier is also included to help understand the principals of thepower detect and hold function.

The primary function of this circuit in the μATS is to detect thepresence of AC power on the “A” side, and hold connection to that powersource in the relay section later described. This circuit also has thedelay control that prevents returning to a power after a transfer forabout 5 seconds. This prevents unnecessary transfers if the “A” sidepower source is intermittent. In addition, this circuit also rejectsmany conditions, such as outages shorter than 4 ms, momentary sags,etc., of power that would otherwise cause false transfers.

The core functionality is achieved by rectifying the AC power via acurrent limiting 0.22 uf capacitor. The rectified power is mildlyfiltered in C6, but the primary function of C6 is to control the amountof hold-over current present during AC outages at the zero crossing ofthe AC line. Otherwise, the μATS would disconnect from the “A” side atevery AC crossing, 120 times a second.

This capacitor is also largely responsible for determining the time fora minimum outage before releasing the latch that controls the “A” sideconnection, and transferring to the Alternate Power Source, (“B” side).

The transistor pair of Q 17 (PNP) and Q18 (NPN) act as a SCR connectedpair. Observing the description of the SCR, and the pair of Q17 and Q18(FIG. 5) demonstrates this configuration.

The thyristor is a four-layer, three terminal semiconductor device, witheach layer consisting of alternately N-type or P-type material, forexample P-N-P-N. The main terminals, labeled anode and cathode, areacross the full four layers, and the control terminal, called the gate,is attached to p-type material near to the cathode. (A variant called anSCS—Silicon Controlled Switch—brings all four layers out to terminals.)The operation of a thyristor can be understood in terms of a pair oftightly coupled bipolar junction transistors, arranged to cause theself-latching action:

Referring to FIG. 5, when current is continuously flowing through the Q17, Q18 pair, it will remain latched “on”. If current is interrupted,the latching will be lost, and it will not conduct again untilre-started. In this circuit, conduction, or “gating” is accomplished viathe charging of C8 via R20, and the resulting eventual conduction ofcurrent through Zener Diode ZD1. This sub-circuit has a time constant ofabout 5 seconds and provides the delay function on start-up necessary toprevent rapid transfers if source power is intermittent. A uniquefeature of using this dual transistor SCR emulation is that access tothe collector of Q17 allows the secondary function of the “SCR” pair byallowing supplemental current to be presented to the base of Q15. Uponsuccessful latching of the “SCR” pair, the timing capacitor C8 is resetnearly to zero voltage by the conduction of Q15. This prepares thetiming circuit for the next off-to-on cycle. Another feature of thiscircuit is that access to the base of Q17 allows insertion of atransient suppression filter and programmed current release pointdetermined by resistors R13, R26 and C7. This is necessary because therelease point of the “SCR” pair must be below the on threshold of theoptical isolator and subsequent amplifier circuit. In other words, it isimportant that the release point be determined by the “SCR” un-latchingrather than the gain of the optical coupler and amplifier.

Additional components include R19, which depletes C6 at a known rate,R21 which guarantees full discharge of C 8 on initial startup, and LED 5(Green), an indicator for the user interface to show that A power is onand is selected for the source of delivery to the output of the μATS.

Another unique feature of this design is it's extremely low powerconsumption. Since this circuit must operate at all times when theprimary power (“A” side) is being delivered to the load, minimization ofpower consumption was of high importance. No external power supplies arerequired, and power through LED 5, and the Optical Isolator LED, isdetermined primarily by the current limiter 0.22 uf capacitor (C3), andthe 56 K pass resistor R2. Other values of Resistance and capacitancecould be selected to further reduce normal function power consumption,but these values are selected for maximum noise immunity and lowestpower consumption in this application.

FIG. 5 demonstrates the initial electrical activity very shortly afterapplication of power to the circuit.

AC power (Teal) is applied to the bridge, converted to rectified DC andcharges C6 and C8. C8 charges slowly towards the conduction threshold ofZD1. No action happens in any other parts of the circuit. This is theinitial delay part of the start up cycle of the “A” side. If the uATSwere returning power from the “B” side to the “A” side after a previousfailure of the “A” side, this delay would provide about 5 seconds tomake sure the “A” side was stable.

FIG. 6 represents the condition just at the conduction threshold of ZD1.At this point the base of Q18 now has voltage being applied to itrelative to the emitter.

Q18 is not yet conducting, as about 0.6 V must be present prior tobeginning of conduction, but the latch is about to set.

At this point, C8 is charged to about 13 V, D19 is conducting and ZD1 isconducting. As C8 continues to charge, eventually base current starts toflow in

Q18, initiating an “avalanche” condition in the “SCR” pair, Q18 and Q17.

FIG. 7 shows the condition of current flow a few microseconds after thebase current starts to flow, and current starts to flow through LED5,the optical coupler LED, R13 and the base of Q17.

Current flows in the base of Q17, thus causing it to conduct and addcurrent to the base of Q18, further turning it on, adding current to thebase of Q17, so on and so on until the pair is “latched” on. This set ofevents occurs very rapidly, and the LED of the optical isolator isturned on very rapidly. Simultaneously, the base of Q15 has voltageapplied to it, and the subsequent current causes Q15 to conduct,discharging C8. The discharge rate of C8 is limited by the base currentlimiter resistor R24.

FIG. 8 shows this state of this circuit during the discharge cycle ofC8, and just before the final state of the circuit prior to normalfunctional operation of the μATS which is the state of delivering “A”Side power to the output.

At this stage, C8 has been discharged below the conduction threshold ofZD1, and hence Q18 is getting its base current solely from the collectorof Q17 via the system current limiting resistor R25.

FIG. 9 shows the normal operating state of the uATS while on the “A”Side power source, the primary power source. The vast majority of theuATS operating time should be in this mode.

FIG. 10 shows the u ATS shortly after the loss of “A” Side Power. Thecircuit continues to operate for a short period by extracting theremaining charge from C6.

As the available power in C6 is depleted, the resistive divider of R26and R13 reaches a point where Q17 begins to not be forward conductingthrough its base, thus reducing the current in it's collector.

This is the start of the rapid cascade to release of the “SCR” pair, Q17and Q18. FIG. 11 illustrates this transient condition.

FIG. 12 shows the condition after the “SCR” pair, Q17 and Q18 havereleased, and are no longer conducting, and hence the LED 5 and theoptical isolator diode are also no longer conducting. At this point theevents controlled by the timing and synchronization circuits areinitiating the transfer to the “B” side of the relays in the A/B relayswitching circuit.

The final electrical activity is the removal of residual current fromthe base of Q18. Also, residual charge in C6 and C8 is depleted viaresistors R19 and R21, respectively. Hence, the circuit is ready for thereturn of “A” power when it occurs.

FIG. 11 shows a circuit diagram of an illustrative “B” powersynchronization detection subsystem 720 a for use in some embodiments ofa micro-ATS 700. “B” power 765 is received as BH and BN, and isfull-wave rectified by bridge BR5. The current is limited by R57. Theoutput of the bridge BR5 drives the diode in opto-transistor U1. Asillustrated, the transistor on U1 will turn off when the output of thebridge BR5 is less than a preset threshold (illustrated as approximately6 volts, though other values can be set if desired). This derives thezero-voltage crossing of “B” power 765, which can then be used forzero-voltage synchronization.

Embodiments of the “B” power synchronization detection subsystem 720,such as the embodiments illustrated and described with reference to FIG.11, provide a number of innovative features. One such feature is thatsome embodiments of the “B” power synchronization detection subsystem720 provide loss detection as a direct function of power availability.As illustrated, the “B” power synchronization detection subsystem 720 ispowered by the source it is detecting. If the power fails, the circuitceases to detect that source and it fails to provide the opticallyisolated control to the timing control subsystem 730 via the “B” powersynchronization detection subsystem 720. This provides a fail-safedesign, in that if “A” power 760 fails, the remainder of the micro-ATS700 circuits default to transferring to “B” power 765.

Another such feature is that some embodiments of the “B” powersynchronization detection subsystem 720 provide noise and falsetriggering immunity. As illustrated, the circuit has a power envelopedetect methodology. C6 is continuously charged by the incoming power andcontinuously discharged by the A Loss Detect circuits and by the LED inthe optical isolator U2. Thus, for a valid power loss to be detected,the capacitor C6 must discharge its energy to allow the transfer. Oneresult is that it stores the energy during each half-cycle allowingeasily programmed delay timing between the time that power fails and thetime that initiation of transfer actually occurs. Another result is thatunwanted glitches are filtered where they would otherwise cause falsetransfers. Yet another result is that under-frequency detection isprovided without additional components. If the input frequency of the“A” power 760 side falls below the total envelope charge for a giventime, the capacitor C6 will fail to store enough charge from cycle tocycle, and the latch (formed by Q17 and Q18) will release and allowtransfer of the load to the “B” power 765 side.

FIG. 12 shows a circuit diagram 1200 of an illustrative “A”/“B”synchronization integrator subsystem 725 a in context of the “B” powersynchronization detection subsystem 720 and the “A” power loss detectsubsystem 715 for use in some embodiments of a micro-ATS 700.Embodiments of the “A”/“B” synchronization integrator subsystem 725 aprovide synchronization of “B” to “A” transfers at zero voltage crossingtimes and the “A” to “B” integration function. For the sake of clarity,functionality will be described during start-up, during a transfer from“B” power 765 to “A” power 760, and during a transfer from “A” power 760to “B” power 765.

Turning first to functionality during start-up, “A” power 760 is turnedon. Accordingly, “A” power 760 will be present at the output because “A”power 760 uses the NC (Not Connected) contacts of the relays. After somedelay (illustrated as approximately 4 seconds), the “A” power lossdetect subsystem 715 will light its indicator LED (LED 5) and providecurrent for the diode in U2. The transistor in U2 will turn on andprovide a current path for R15 and R11 to turn on Q33. Q33 will thenprovide a current path through R28 and D23 to charge the integratorcapacitor C9. Q33 will also turn Q19 on and will be helped by thecathode of D16 going positive, providing positive bias through D14 andR62. When Q19 turns on, Q20 will turn off disabling the “B” powersynchronization detection subsystem 720. Thus, the opto-transistor in U1will have no influence on the charge of the integrator. Currentcontinues to flow from the collector of Q33 to C9 via R28 and D23charging C9. This is the initial charge integration signal to be sent tothe timing control subsystem 730 for threshold detection there. As thecharge builds, it eventually reaches a point where the comparators (U3 aand U3 b) detect the crossovers. This is the basis of establishing thetiming spaces between the events of the relays switching. The interrelay transfer timing of transfer from B to A is essentially controlledby R28.

Turning to functionality during transfer from “B” power 765 to “A” power760, much of the functionality is essentially the same as that describedabove with reference to the start-up functionality. Approximately 4seconds after “A” power 760 returns, the indicator LED (LED 5) willlight (i.e., this is similar to when “A” power 760 is initially startedup, as described above). Current will go to U2 and turn U2 on. Q33 willturn on, starting to charge U9. At this point, Q20 and U1 are turned on,and Q19 is turned off and cannot turn on until the next zero crossing of“B” power 765 when U1 turns off. This allows the anode of D22 to gohigh, turning Q19 on, turning Q20 off, and slowing the integrator tocharge through R28. This causes the micro-ATS 700 to switch to “A” power760.

Turning to functionality during transfer from “A” power 760 to “B” power765, if “A” power 760 should fail, U2 will turn off, causing Q33 to turnoff. This will turn Q19 off and Q20 on. Since the opto-transistor in U1is almost always conducting, Q20 and the opto-transistor in U1 willshort the integrator through D24 and R70 at any time except exactly atthe next zero crossing of the “B” power 765 side. As C9 rapidlydischarges, the integrator output to the timing control subsystem 730will cross over the thresholds of the comparator U3 a and U3 b. Thefirst event will be to set RY On via U3 a. Since U3 b is presentlybiased to provide the shunt at the junction of Relays RY2 and RY3, highinrush current will flow in RY2, causing it to disconnect the “A” power760 from the load. As the integrator voltage continues to fall, thesecond comparator threshold is passed, and U3 b releases GC On. Thisde-energizes the gatekeeper relay (RY3) and the Neutral Relay (RY1)shunt. Then, very shortly thereafter the Gatekeeper relay (RY3) and theNeutral Relay (RY1) will connect the load to the “B” power 765 ACsource. Only then does current start to flow to the load from the “B”power 765 AC power source.

Embodiments of the “A”/“B” synchronization integrator subsystem 725,such as the embodiments illustrated and described with reference to FIG.12, provide a number of innovative features. One such feature is thatsome embodiments of the “A”/“B” synchronization integrator subsystem 725provide very high efficiency, for example, because of their use of highimpedance components to reduce size and minimize power consumption.Another such feature is that some embodiments of the “A”/“B”synchronization integrator subsystem 725 act as a multi-function circuitto minimize component count. As illustrated, embodiments combine thefunctions of synchronizing the return from “B” power 765 to “A” power760, and the timing control for the gap between disconnecting the “A”power 760 before connecting the “B” power 765 to the outputs. Bycombining these functions, parts count can be minimized and the overallsize of the finished product can be reduced. Yet another such feature isthat some embodiments of the “A”/“B” synchronization integratorsubsystem 725 provide power off delay timing during transfer from “B”power 765 to “A” power 760. The transition time power off delay isaccomplished via an easily programmed capacitor value (C9). C9 is theintegration storage capacitor that supplies threshold ramp signal to U1,the timing comparator. Adjustment of C9 changes the delay between the Adisconnect relay (RY2), and changing state of the Gatekeeper (RY3) andNeutral (RY1) relays.

FIG. 13 shows a circuit diagram of an illustrative timing controlsubsystem 730 a for use in some embodiments of a micro-ATS 700.Comparators in embodiments of the timing control subsystem 730 controlswitching functions of the relays and activation of the warningindicators and buzzer. The ladder formed by R45, R46, and R47 definesvoltages V1 and V2. Integrator (C9) is the output of the “A”/“B”synchronization integrator subsystem 725, and is high when the micro-ATS700 is using “A” power 760 and low when the micro-ATS 700 is using “B”power 765. The slope of the transition from “A” power 760 to “B” power765 and from “B” power 765 to “A” power 760 is controlled by C9 and R70,and by C9 and R28, respectively. C9, R70, and R28 are discussed as partof the “A”/“B” synchronization integrator subsystem 725.

Pin 2 of the comparator U3 a is the Relay On (Low) signal and drives theemitter of Q29. Pin 2 will subsequently apply HV power to the A relayRY2 (RY On). Pin 1 of the comparator U3 b is the GC Shunt Drive (Low)and drives the emitter of Q14. Pin 1 will subsequently ground the otherside of the A relay (RY2) when asserted. This applies the full HV power(150 Volts) across the A relay (RY2), which can assures fast operationof the A relay (RY2). Times T1 and T2 are controlled by V1 and V2, andby the rising and falling slope of the Integrator (C9).

Embodiments of the timing control subsystem 730 participate in “A” power760 to “B” power 765 transitions according to the following technique.When “A” power 760 fails, the Integrator (C9) will start to ramp down toV1. HV power will then be applied to RY2. Ground is already on the otherside of the RY2 coil. RY2 will then disconnect from the “A” power 760side. When the Integrator (C9) drops further to A2 (the end of time T1),the signal GC Shunt Drive will go high releasing the ground from RY2 andallowing current to flow through RY2 to RY1 and RY3. This connects “B”power 765 and Neutral Out to the output power 770 node. Time T1 assuresthat “A” power 760 is released before “B” power 765 is connected.

Embodiments of the timing control subsystem 730 participate in “B” power765 to “A” power 760 transitions according to the following technique.At the beginning of T2, RY2 is grounded, removing power from the RY1 andRY3 relays. This connects the Neutral Out (NO) to “A” Side Neutral (AN)and Hot Out (HO) to the RY2 relay, which is open at this point. At theend of T2, HV power is removed from the RY2 relay, thus connecting “A”Side Power to the Hot Out (HO). HV and “Common 2” are the outputs of theHV power supply. During normal operation, Common and Common 2 areconnected together by the Darlington transistor Q22.

Embodiments of the timing control subsystem 730 participate inover-current control according to the following technique. When theoutput current approaches a pre-defined warning point (e.g., between 12and 13 Amps), an indicator is illuminated to warn the user that this isthe maximum advisable limit for continuous current. At this point V3 andV4 are defined by the ladder resistors R34 and R36 and diode D7 asdiscussed above. Output current is detected in the output current detectsubsystem 740, and an analog voltage is generated there and sent to thetiming control subsystem 730. The slope of the “Load Current SensedSignal” (LCSS) is a function of applied current to the attached load andtime. V4 is set to be equivalent to approximately a 12-Amp load on theoutput of the micro-ATS 700 (or another desired value). When the LCSSexceeds V4, pin 13 of comparator U3 d will go low. This will cause aloss of conduction through ZD7 guaranteeing that Q22 will turn off whenU3 d pin 13 goes low, which, in turn, will energize the indicator LED(LED4). R37 and D13 will cause V4 to drop slightly increasing theseparation between V4 and the LCSS. C25 also serves to smooth out thedifference between V4 and the LCSS.

If the LCSS then drops below V4, LED4 will turn off. If, however, theLCSS continues to increase to V3, pin 14 of U3 c will go low. This cancause three events to occur. One event occurs because D26 and D27 areconnected to U3 a pin 2 and U3 b pin 1. When U3 c pin 14 goes low, pins2 and 1 are also pulled low. This activates RY2, disconnecting the powerfrom the output via D26, and locks out the shunt drive from activatingvia D27. Another event is that the piezoelectric device driver subsystem750 will be turned on via the negative supply path. Another event isthat Q23 will be turned on by R41. Q23 will pull the LCSS to 15 volts,latching the fault signal low. Q23 is discussed further with referenceto the piezoelectric device driver subsystem 750.

According to some embodiments, when the micro-ATS 700 output currentexceeds the pre-defined limits (e.g., substantially like a 14.5-Ampfast-blow fuse), an indicator is illuminated that indicates themicro-ATS 700 disconnected the load from the source, and a buzzer soundsto warn the user that the micro-ATS 700 has disconnected the load. Thisprovides “virtual circuit breaker” (VCB) function of the micro-ATS 700.

At this point V3 and V4 are defined by the ladder resistors R34 and R36and diode D7, as discussed above. If an over-current condition occurs,the LCSS will be detected by the timing and control comparators U3C andU3D. If it represents a current of greater than 15 A for 10 seconds, the“Fault (Low)” signal will be generated, latching Q23 and charging C12.This will protect fuses F1 and F2. If the overload is removed and switchSW1 is pressed, the charge on C12 will be transferred to C13. Q23 willbe turned off and power will be restored to the output. If, however, theoverload has not been removed, then C15 is still charged, so that “FaultLow” will be regenerated, and Q23 will be turned back on. Repeatedpressing of the reset switch (SW1) will charge up C13 from C12 andnothing will happen. This prevents an already hot F1 or F2 from gettingrepeated hits when SW1 is pressed. Thus the virtual fuse protects theinternal real fuse.

Embodiments of the timing control subsystem 730, such as the embodimentsillustrated and described with reference to FIG. 13, provide a number ofinnovative features. One such feature is that some embodiments of thetiming control subsystem 730 provide very high efficiency. Embodimentsuse very low-power components and high-impedance circuits to minimizepower consumption. Another such feature is that some embodiments of thetiming control subsystem 730 provide high voltage control. Theconnection of the low-voltage, low-power control section to thehigh-voltage relay-power control section is accomplished via aninnovative coupling using a variation of the grounded baseconfiguration, where the bases of Q14 and Q29 are referenced to the+15-Volt power supply. The emitters of those transistors are connectedto the open collector outputs of U3. Since these outputs are onlycurrent sink to the common supply and that they also cannot be exposedto voltages greater than the plus supply, these voltage amplifiertransistors (Q14 and Q29) provide that voltage amplification with as fewcomponents as is possible.

Yet another such feature is that some embodiments of the timing controlsubsystem 730 provide power savings in LED illumination of the indicatorLEDs (LED 4 and LED 1).

The improvement in efficiency is not so much the savings of power whenthe LEDs are illuminated, as this is the time when there is either afault or a undesired condition, and is not the predominant operatingcondition of the micro-ATS 700. However, the fact that the innovativeway of powering these LEDs eliminates the need for an additional powersupply, and the attendant losses associated with such an addition, is animprovement in efficiency. Both of these LEDs are powered by currentthrough the rest of the circuitry that is utilized, regardless of theconditions of the LEDs otherwise. The current is being passed throughLED 4 from the current utilized to operate the timing control subsystem730. When not needed (not illuminated) LED 4 is turned off by theshorting transistor Q22. The only condition when a fault is necessarilyindicated (e.g., by LED 1) is when the A relay (RY2) is active, and theGatekeeper and Neutral relays (RY3, RY1) are shunted into the offcondition, thus disconnecting power from the source to the output. Inthis continuous condition, the current necessary to power the A relay(RY2) is passed through LED1. This current path is already necessary topower the relay, thus it can be used to power the LED with no additionalpower supply circuitry. This design feature reduces power consumption,and simplifies the total design.

FIG. 14 shows a circuit diagram of an illustrative “A” & “B” powerswitching subsystem 735 for use in some embodiments of a micro-ATS 700.The “A” & “B” power switching subsystem 735 controls when the selectedpower source to the micro-ATS 700 is switched, either from “A” power 760to “B” power 765 or “B” power 765 to “A” power 760. Embodiments alsocontrol over-current condition switching and relay sequencing, usingRY1, RY2, and RY3 to control the flow of power from the “A” power 760and “B” power 765 inputs to the output power 770 node. Both “A” power760 and “B” power 765 can be protected by fuses F1 and F2, respectively.

One condition of the “A” & “B” power switching subsystem 735 that isworth discussing is during an inter-transfer time (e.g., which may besubstantially similar or identical to the condition of the “A” & “B”power switching subsystem 735 under a fault condition). When GC On 825goes low (U3 pin 1) as discussed with reference to the timing controlsubsystem 730, R52 will provide the bias to turn Q14 on. Current in thecollector of Q14 will bias the base of Q16 and in turn will turn Q16 onvia R55. This is the voltage amplifier from the 15-Volt limited outputof U3 to the 150-Volt offset to Q16 and Q4. The current in the emitterof Q16 is passed through the base of Q4 and to the coils of RY2 and RY3,thereby grounding them (as discussed more fully above). At this point,only the A relay (RY2) is energized. The function of Q4 will bediscussed below with reference to the disconnect switch subsystem 745.According to the illustrated embodiment, transfers from “A” power 760 to“B” power 765 and from “B” power 765 to “A” power 760 may take around 2milliseconds. It is also the state of the micro-ATS 700 during a faultcondition (e.g., an over-current detected condition). It is worth notingthat there is no AC Hot path from either “A” power 760 or “B” power 765to the output power 770 node in this condition.

Another condition of the “A” & “B” power switching subsystem 735 that isworth discussing is when power is transferred to the “B” power 765source. When “Relay Power (Low)” goes low (U3 pin 2) as discussed withreference to the timing control subsystem 730, R66 will provide the biasto turn Q29 on. This is the voltage amplifier from the 15-Volt limitedoutput of U3 to the 150-Volt offset to Q30. The current in the collectorof Q29 will turn Q30 on via R67. This will provide 150-Volt “HV” powerto the 48-Volt coils of the series-wired relay string (RY1, RY2, andRY3).

FIG. 15 shows a circuit diagram of an illustrative disconnect switchsubsystem 745 a for use in some embodiments of a micro-ATS 700. Thisswitch is used to disconnect the alternate power source (via node A2775) from the power supply subsystem 705 when not required. According tosome embodiments, application of the alternate power source occurs onlyin one condition. When the micro-ATS 700 has a fault condition present(e.g., over-current), the relays of the “A” & “B” power switchingsubsystem 735 are configured with the A relay (RY2) in the disconnect(i.e., energized) position, and the Gatekeeper relay (RY3) and theNeutral relay (RY1) in the disabled (i.e., non-energized) position. Thusno output voltage is available at the H or N nodes, and the micro-ATS700 would not have power input to the power supply subsystem 705. Inthis case, the normally open contact of the A Relay (RY2) has powerpresent on it, which is directed to the power supply subsystem 705 viaA2 775 to maintain power to the power supply subsystem 705 in thiscondition.

During all other states of the micro-ATS 700, it may not be desirable tohave this connection. Differences in voltages between the A2 775 signalwhen the A relay (RY2) is energized and the “B” power 765 for the powersupply subsystem 705 will cause transitory currents to be distributedunevenly between the AC hot power sources and their respective neutralreturn paths. This can result in possible interruption of a source powercircuit served by a Ground Fault Circuit Interrupter (GFCI) receptacleor a circuit breaker. To prevent this condition, the disconnect switchsubsystem 745 only allows alternate power via the A2 775 node toactivate when a fault condition is present.

According to the illustrated embodiment, during a fault condition, thebase of Q4 is pulled negatively by the output of the timing controlsubsystem 730 and the voltage amplifier via the signal GC On 825.Current through the base of Q4 to the emitter thus clamps off currentthrough the Gatekeeper relay (RY3) and the Neutral relay (RY1). At thesame time, RY Power On 820 is active to energize the via the emitter andbase of Q4 to GC On 825, which is pulled to round. In this state, the Arelay (RY2) is on (i.e., energized), and the Gatekeeper relay (RY3) andthe Neutral relay (RY1) are held off. It is worth noting that, in thiscondition, there is no source of power available to the output power 770node. This is the state of the relays during a “fault” condition (e.g.,an over-current state).

In the event of a fault condition, in the timing control subsystem 730(described above), the indicator LED (LED 4) is on, and Q22 is not on.In addition, the indicator LED (LED 1) is turned on by the current intothe base of Q4. The sum total of the voltage from the cathode of theindicator LED (LED 4) to the HV Common 815 exceeds the threshold ofZD11. The current through ZD11 (green) thus illuminates the LED in U5,providing current to the base of Q3. Q3 then conducts and “shorts” outboth conduction paths through BR6 allowing AC power to pass from C16 toA2 775. A2 775 then supplies the power supply subsystem 705 with ACsource power only during a fault condition. C16 limits the total ACcurrent to the power supply since, during this one condition, the Arelay (RY2) is the only relay that is energized.

It should be noted that the reset switch SW1 in the Timing ControlSubsystem can be connected to have additional functionality. In thismode two switches are used, one of which is the existing “reset” buttonwhich re-initiates power connection to the output after a faultcondition, and one is an additional switch and associated latchingcircuit, used to clear the latching circuit if it is in the “off” modeand turn it back on. Thus the “off” switch will essentially “trip” theVirtual Circuit Breaker, by initiating the clear state (i.e. “off”)condition without sounding the piezoelectric buzzer. This is done byconnecting the off switch controlled latch to the control node betweenthe present fault detect circuit and the relay control circuit. The modeof connection is commonly known as “wired OR”.

Embodiments of the disconnect switch subsystem 745, such as theembodiments illustrated and described with reference to FIG. 15, providea number of innovative features. One such feature is that someembodiments of the disconnect switch subsystem 745 provide very highefficiency. As illustrated, the use of three relays in series, rated at48 volts each, can allow the application of directly rectified AC mainsvoltage to the relays. This eliminates additional power conversioncircuitry, thus reducing parts counts as well as increasing efficiency.Another such feature is that some embodiments of the disconnect switchsubsystem 745 use current limiting capacitor (C16) when only the A relay(RY2) is activated continuously, which allows use of the otherwiseunused “normally open” contact of that relay, and further reduces partscount.

Yet another such feature is that some embodiments of the disconnectswitch subsystem 745 provide relay sequencing when all three relaysrelease simultaneously to prevent arching. As illustrated, the couplingof the fly-back suppression diode D48 on RY2 to the return path ratherthan directly across the relay provides a slight contact timing delaybetween the A relay (RY2) losing power and the Gatekeeper relay (RY3)and Neutral relay (RY1). This is accomplished by the anode of D48 beingconnected to the common rail instead of the more traditional connectionto the relay coil. In this configuration, the A relay (RY2) has a higherimpedance for the fly-back current to sink into, as the sinking currentis also going through RY1 and RY3. The higher impedance results in therelay armature being able to move less quickly then the armatures of theother two relays. The result is that when the power is disconnected fromthe relay chain, RY2 will always connect the “A” power 760 slightly indelay to the disconnection timing of the gatekeeper (RY3) from the “B”power 765. This helps insure that “A” power 760 never becomes connectedto “B” power 765 simultaneously while relay contacts are still together.Even if there is sufficient current to force a small arc, the relaycontacts have disconnected prior to the arc starting, thus preventingthe contacts from “welding” themselves in place and causing the “A”power 760 and “B” power 765 to flow uncontrollably. The result of this,in a polyphase application of “A” power 760 and “B” power 765 wouldresult in a blown fuse.

FIG. 16 shows a circuit diagram of an illustrative output current detectsubsystem 740 a for use in some embodiments of a micro-ATS 700.Embodiments of the output current detect subsystem 740 a detect andmeasure the presence and various characteristics of the output currentfrom the automatic transfer switch. This also circuit tends to mimiccharacteristics of a fuse, but only slightly below the thresholds of15-Amp Fast Blow physical fuses that may be used in the “A” power 760and “B” power 765 inputs to the micro-ATS 700. This allows the micro-ATS700 to protect itself without blowing actual physical fuses, which mustbe replaced.

As illustrated, the neutral out of the micro-ATS 700 has a current sensetransformer on it. This transformer has a diode bridge, formed by D28,D29, D30, and D31, which full-wave rectifies the “Load Current SensedSignal” (LCSS, described above with reference to the timing controlsubsystem 730). C22 and R48 filter out the higher frequencies of the ACcurrent and provide proper impedance loading of the current transformer.R11 and Thermistor RT1 provide thermal compensation so the micro-ATS 700can remain accurate over a wide range of temperatures. C14, R50, D32,D3, C15, R51, and R75 can be configured and selected to effectivelyemulate the time VS current opening threshold of a 14.5-Amp fast-blowfuse, with the time part of the curve advanced to open about 33% fasterthan the equivalent 15-Amp fast-blow fuse.

Embodiments of the output current detect subsystem 740, such as theembodiments illustrated and described with reference to FIG. 16, providea number of innovative features. One such feature is that someembodiments of the output current detect subsystem 740 employ acombination of capacitors and resistors that result in an analogrepresentation of the characteristics of a fast blow fuse. The principalcharacteristics of the timing of a fuse are as follows: it can carrysignificant over-current for a short period of time; and, after sometime, the fuse will “blow” at or near the rated current of the fuse.This is primarily controlled by the thermal characteristics of the fusematerial itself, and how much mass is being heated to the melting pointby the applied current. In order to emulate the characteristics of afuse, a pseudo two-pole filter is formed by these components to emulatethe desired characteristics. The circuit reduces the parts count to theminimum by having the two halves of the two poles interact with eachother by allowing current from the first pole to charge the second polewithout the reverse. The second pole is discharged by a controlleddischarge path through R32. This single point of discharge can thus beused to bias both poles of the filter and alter the overall curve of theresponse time of this circuit without significantly changing the shapeof the curve. This is useful for adjusting the “rating of the fuse” by asimple one component change, specifically R32. By changing the value ofR32, the programmed threshold of maximum current rating of theelectronic, or virtual, fuse (circuit breaker) can be adjusted simplyand with minimum effect on the inrush current handling characteristicsof the circuit.

Another such feature is that some embodiments of the output currentdetect subsystem 740 provide temperature stability. Numerous variablesare introduced into the design of the virtual circuit breaker design(e.g., as discussed with reference to the output current detectsubsystem 740 and to the timing control subsystem 730 above) that affecttemperature related stability. Compensation of all of the thermalvariables as well as emulating the thermal effects in a real fuse isaccomplished by RT1 and R11. RT1 is a thermistor that has a negativetemperature coefficient. As temperature goes up, the resistance goesdown, in a predictable fashion. By placing these two components inseries across the current sense transformer, the load impedancepresented to that transformer is affected by temperature. The selectionof values for the Thermistor RT1 and R11 result in the overallperformance of the virtual circuit breaker effectively mimicking itselectro-mechanical equivalent.

FIG. 17 shows a circuit diagram of an illustrative piezoelectric devicedriver subsystem 750 a for use in some embodiments of a micro-ATS 700.Embodiments of the piezoelectric device driver subsystem 750 a includean innovative implementation of a power driver for driving apiezoelectric buzzer (or similar device). When “NOT FAULT” goes low, itprovides a ground path for the oscillator formed by Q25, Q27, R40, R42,R44, R39, C10, and C11.

When power is applied, either Q25 or Q27 will turn on. If Q25 turns on,the voltage on both sides of C10 will drop, thereby providing a low tothe base of Q27 and turning Q27 off. Then C10 will charge up via R44.When the voltage at the base of Q27 reaches approximately 0.6 volts, Q27will turn on. Both sides of C11 will drop. Q25 will turn off, and so on,back and forth. Q21 and Q26 are emitter followers. As the collector ofQ25 charges up when Q25 is off, Q23 emitter will follow its base drivingthe piezoelectric buzzer. When Q25 turns on it will sink connect fromthe piezo through D2, and similarly for Q26, D4, and Q27.

Embodiments of the piezoelectric device driver subsystem 750, such asthe embodiments illustrated and described with reference to FIG. 17,provide a number of innovative features. One such feature is that thecircuit provides high efficiency with a low parts count. As illustrated,high efficiency is achieved by combining the oscillator and amplifiernecessary to drive the piezo into a power oscillator, and thecombination also tends to minimize parts count. In this configuration,nearly all the current expended in the circuit for both the oscillatorfunction and the power amplifier function is applied to the piezocrystal for conversion to acoustic energy.

The various circuits and other embodiments described above form novelembodiments of micro-ATSs 700 and provide a number of features. One suchfeature is ultra-low power consumption. Use of a transformer-less powersupply reduces overall loss in converting from 120 VAC mains voltage toDC voltages required for internal circuits. Another such feature is thatvirtually no power is consumed on the non-connected side (e.g., on the“B” power 765 side when the load is connected to “A” power 760). Yetanother such feature is that the use of optical isolation in the powersupply virtually eliminates cross currents between the “A” power 760 and“B” power 765 inputs. Still another such feature is that arc suppressionis provided at the disconnection of the “B” power 765 side on thecontacts of the affected relays by timing the break of the relaycontacts at the zero crossing of the current presented to thosecontacts.

Additional features are realized by selections of certain circuitcomponents and/or topologies. One such feature is that ultra low powerconsumption can be achieved by utilizing a capacitor current limit onthe AC input. The selected capacitor (0.22 uF) limits 60 Hz to about 10milliamps into the 48-volt load. At 50 Hz, the limit is 8 milliamps,both within operating range of the connected relays. Another suchfeature is that use of the same path of current in the “A” power lossdetect subsystem 715 for illuminating the “on A” indicator, activatingthe optical isolator link to the synchronization circuit, and the holdlatch, minimizes the normal operating state draw on the “A” power 760side.

Another such feature is that power delivery from the “A” power 760 sideto the Load, the predominant path of power for the majority of use withregards to time, is via the Normally Closed position of the routingrelays. This eliminates the current necessary to activate the relays.Another such feature is that conversion of the AC mains voltage directlyto DC without the use of a transformer, or power conversion, for thepurpose of minimizing power consumption, is made possible by thearrangement of the relays when activated. Three relays are connected inseries when activated to transfer the load to the “B” power 765 side.This action allows the use of high voltage (AC Mains Voltage directlyrectified to 150 VDC). This design methodology allows thetransformer-less power supply to be implemented.

Another such feature comes from use of the Normally Open contact of theA disconnect Relay (RY2) as an AC Mains diversion path for and alternatepower source during a fault condition. In this condition, only the Arelay is activated. The alternate path described allows a secondrectifier and a capacitor current limit on the AC Mains, so the currentrating of the coil of the single activated relay (RY2) is withinoperating range of 8-10 milliamps. Another such feature is that use oftotal circuit pass current on the low voltage timing control subsystem730 to energize the indicator LED (LED 4) that indicates approaching theover current condition, and shunting the LED to the off condition whennot in use, eliminates the need for an auxiliary power supply for thisdevice. This increases the efficiency of power utilization in themicro-ATS 700, and lowers quiescent dissipation. Another such feature isthat using relay pass current to activate the indicator LED (LED 1) whenin an overload condition also eliminates need for an auxiliary powersupply to power the LED when required. This improves efficiency andreduces normal operating condition power dissipation.

Another such feature arises in the context of “A” power loss detectionthrough an innovative use of an arrangement of semiconductors to performmultiple functions. The arrangement of Q17 and Q18 is similar to asilicone controlled rectifier (SCR). The primary working characteristicof this configuration is that the SCR simile requires very littlecurrent to cause to latch into a conduction state. This latched statewill continue until passing current through the pair ceases. When itceases, the latch will disconnect and not allow current to flow untilre-initiated. In addition, the otherwise inaccessible second PN junctionof the SCR simile is accessible, thus allowing the action at this pointto also affect Q15 at a certain point in the sequence to be beneficial.The Q15 is the timer reset for delaying the return to “A” power 760 froman “A” loss state. This must be reset every time the SCR simile goesinto conduction. By tapping the SCR simile at the collector of Q17 (thebase of the Q18 junction), normally an inaccessible junction in aconventional SCR, the avalanche activation of the SCR simile at thattime can be utilized to force the reset of the timing capacitor C8 viaQ18.

Another such feature arises in the context of synchronization of thereturn from “B” power 765 to “A” power 760 at the zero-crossing of the“B” power 765 signal to reduce arching of the B relay contacts. Anoptically coupled synchronization pulse and level from the “B” power 765source is used for two functions: to synchronize transfer from the “B”power 765 to the “A” power 760 at the zero-crossing of the “B” power765; and to provide a source of signal that indicates the loss of the“B” power 765 and thus force the connection to the “A” power 760,regardless of the state of other circuits that normally would influencetransfers to the “B” power 765 side. First, the optically coupled syncsignal holds off the signal from the optical coupler that indicates that“A” power 760 is ready to be transferred to until the sync pulse appears(via Q19, Q20, and the U1 opto-coupler transistor). After the synchpulse appears at the U1 opto-coupler, the release of the hold on thesignal from Q33 allows the circuit to initiate the integrate functionfor the comparator, U3 to utilize to complete the transfer.Simultaneously, the release of the hold function then latches the syncpulses out so no additional pulses can be present via bias on the baseof Q19. In addition, if there is no AC power present on the “B” power765 side, the output of the sync circuit never presents a low impedanceacross the collector/emitter of the transistor in U1, and hence there isno current sync path for discharging C9, the integrator capacitor. Thus,R33 always holds the integrator capacitor fully charged, and the inputto the comparator presented by C9 will always force selection of the “A”power 760 side, regardless of the state of the “A” power loss detectsubsystem 715 output at U2. This unique approach to providing the syncand holding the output on “A” power 760 if “B” power 765 is not presentutilizes a minimum number parts, each of which operates in highimpedance mode. This reduces power consumption to the minimum, and stillis low cost to produce.

Another such feature arises from the unique piezoelectric device driversubsystem 750. This arrangement of Q21, Q26, Q25, and Q27 forms atransistor pair oscillator. Q25 and Q27 form the basis of an astableoscillator with R39, R40, R42, R44, C10, and C11 forming the componentsthat determine oscillation. The innovative addition of D2, D4, Q21, andQ26 turn the oscillator into a power oscillator capable of driving piezocomponents bilaterally (e.g., one side of the Piezo is at +15, while theother is at Common; then it switches, and the opposite is true). Thismaximizes the output to the Piezo for a given power supply voltage, atminimum parts count and minimum power dissipation. This same poweroscillator can be used for other applications such as driving aminiaturized switching power supply, or for signal source in a smalltester. Numerous applications exist for a miniature, low power, very lowcost power oscillator.

Various changes, substitutions, and alterations to the techniquesdescribed herein can be made without departing from the technology ofthe teachings as defined by the appended claims. Moreover, the scope ofthe disclosure and claims is not limited to the particular aspects ofthe process, machine, manufacture, composition of matter, means,methods, and actions described above. Processes, machines, manufacture,compositions of matter, means, methods, or actions, presently existingor later to be developed, that perform substantially the same functionor achieve substantially the same result as the corresponding aspectsdescribed herein may be utilized. Also, as used herein, including in theclaims, “or” as used in a list of items prefaced by “at least one of”indicates a disjunctive list such that, for example, a list of “at leastone of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., Aand B and C). Further, the term “exemplary” does not mean that thedescribed example is preferred or better than other examples.Accordingly, the appended claims include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or actions.

Extremely Efficient Data Center Power Distribution A method is describedto implement extremely efficient data center power distribution usinghighly parallel auto-switched power at ratios of 1 μATS™ to 1 EDP deviceor 1 μATS™ to a low integer number of EDP devices) as described earlier.This method is also much more reliable than other methods of using ATSdevices for power distribution.

Extremely Efficient Rack Space Usage

If the ATS technology used to implement the highly parallelauto-switched data center power distribution has a sufficiently smallform factor, it is possible to implement the methodology without usingany rack space that could otherwise be used for mounting EDP equipmentby placing the ATS units in various locations as follows:

Mounted on and fitting within 1 U or near the EDP equipment beingpowered

Integrated into the structure of the rack

Mounted near the rack, for example on top of it

Integrated into EDP equipment.

Integrated into an in-rack or near rack PDU such as the ZPDU. Eachsub-branch output of the ZPDU would normally be auto-switched in thiscase.

The described example μATS™ is sufficiently small to be placed in theselocations.

Increased Efficiency Data Center Power Distribution

A method that increases the efficiency of traditional data center powerdistribution using auto-switched power as described earlier. This isdone by using μATS™ devices to “shift” electrical loads in a data centeronto one of a pair of UPS units, so that all of the load is taken byonly one of the UPS units. This increases the efficiency of the UPSunits by insuring that one of the UPS units is running at greaterefficiency and the other is running at or close to zero load, where itconsumes very little energy.

In the following description, numerous specific details are set forth toprovide a thorough understanding of the present invention. However, onehaving ordinary skill in the art should recognize that the invention maybe practiced without these specific details. In some instances,circuits, structures, and techniques have not been shown in detail toavoid obscuring the present invention. Embodiments are described withrespect to various systems, components, and processes for use in a datacenter environment, though it will be appreciated that various aspectsof the invention are applicable in other contexts. For example,embodiments may be advantageous in designing power distribution forserver farms, such as those used by large information services or cloudcomputing providers. Moreover, for convenience of reference, varioussystems, components and methodology are identified by goods and/orservices offered under the Zonit trademark, which is owned by ZonitStructured Solutions, LLC, the assignee of the present application.

Embodiments provide techniques for delivering auto-switched power usingmultiple automatic transfer switches (ATSs) and/or parallel modular ATSswitches to end-user equipment mounted in data center racks. In someimplementations, the design and construction is facilitated by theoptional use of hydra cords to create a power distribution system in therack that allows the dimensions of the rack to be optimized to maximizethe efficiency of the use of data center floor space. Accordingly,airflow can be optimized in the equipment rack by minimizing the numberof power cables needed and their routing in the rack. Certainembodiments further include other power distribution technologies thatunite auto-switching capabilities with power phase load balancing.

Typical modern data centers can have power distribution networks thatinclude thousands of branch distribution circuits. Precise loadingand/or demands of the various electronic data processing (EDP) equipmentis often unknown to the data center personnel. Accordingly, changes tothe loading of these circuits can cause electrical failures, forexample, when branch circuit breakers are tripped by personnel pluggingin a load that exceeds the capacity of the circuit. Further, it may beimportant to maintain loading of each branch circuit at or below about75% of its capacity to account for “inrush loads” that can occur duringa cold start, which may be the highest load scenario and can otherwisetrip the branch circuit breakers when it happens.

Downtimes or failures of EDP equipment in a data center can beundesirable for a number of reasons. One reason is that these EDPdevices can support mission-critical or life safety goals, for whicheven a short interruption in functionality can be catastrophic. Anotherreason is that inter-dependencies of modem IT infrastructures and theirapplications are quite complex and may not always be fully appreciated.A single EDP device may provide an underlying service that nobodyrealized was associated with that device, and a power loss can causelarger business functions that depend on the affected service to beadversely and expensively impacted.

Yet another reason that downtimes or failures of EDP equipment in a datacenter can be undesirable is that restarting an IT infrastructure andthe applications that run on it successfully, from either a cold-startor intermediate state, can be very site-specific and unpredictable. Mostenterprise sites never test this aspect of their information systems.Often proper startup procedures rely on a specific sequence and timingof network, system, and application services. In any complex enterpriseenvironment, all services do not usually recover normally if you powereverything up at the same time. Similarly, problems can arise if youpower down and power up particular sub-components. Restoring properfunctioning of the functionality may involve extensive humanintervention, including manual reboots or service stop/starts. Further,EDP equipment downtimes can be significant, can be difficult to diagnoseand fix, and can cause corruption of service configurations or data insome instances.

Many types of EDP equipment may be particularly vulnerable to electricalfailures at the branch circuit. For example, many models of EDPequipment have only one power supply, and therefore one power cord.Thus, a failure of the input power to the power cord interrupts power tothe power supply of the equipment. One technique for improving powerdistribution reliability for EDP equipment is to offer configurationshaving multiple power supplies. However, even in equipment havingmultiple independent power supplies, interruption of the input power cancause failure (or downtime) of the equipment when the device can only beplugged into one power source at a time.

Implementations with multiple power supplies can have additionallimitations. One limitation is that additional power supplies raise thecost of the device and can be associated with minimum additional amountsof power loss associated with running those additional supplies. Anotherlimitations is that power supplies, especially the types typically usedin EDP equipment, function most efficiently in a relatively narrow bandof their output load rating (e.g., 70-85%). If an EDP device is offeredin single and dual power supply configurations, the product manager maynot wish to stock two different models of power supply with differentload range optimizations, since that can represent additional expense tothe manufacturer. This often means that the product manager will chooseto stock the single power supply optimized configuration, which isoptimized for perhaps a 70% load. When this power supply is specified ina dual power supply configuration, it will then be running at around 50%of its optimal loading, thereby appreciably lowering its efficiency.

A different approach to addressing the issue of power distributionreliability is to implement EDP equipment with auto-switching powerplugstrips. Typically, those plugstrips are bulky and expensive, andthey are usually mounted horizontally in data equipment racks, which cantake up valuable rack space (they tend to take even more rack space withtwo input power plugs connected to two different power sources). Still,enabling auto-switched A-B power delivery to EDP equipment even havingonly a single power supply can appreciably increase the uptime of suchequipment (though not typically to the level of dual power supplyconfigurations). In many cases, this gain in reliability can be enoughto meet the service level availability goals for the applications thatthe EDP equipment supports.

Accordingly, single power cord devices can realize significant gains inuptime reliability when connected to two independent power sources.These sources can be specified to gain the optimum cost benefit toreliability gain ratio. For example, implementations include datacenters with uniform, redundant A-B power distribution, such as thatsupplied by the Zonit Power Distribution System.

A number of data center configurations are possible. One illustrativeconfiguration includes two independent uninterrupted power sources(UPSs). This is often considered the highest reliability scenario, andis a common data center configuration.

Another illustrative data center configuration includes one line powersource and one UPS. This type of configuration may be used as a costsavings measure when the total power usage in the data center exceedsthe UPS capacity or to achieve higher power usage efficiency, since UPSunits have a loss factor for the power they supply. The EDP equipment inthe data center can be connected to run off of line power and onlyselected mission critical equipment is connected to the UPS as a backuppower source. The majority of equipment is just line powered with apower conditioner module to stop input surges. For example, if the sitesteps down industrial power delivery from 480V to a more standard 208V,then a transformer is already in-line and any further power conditioningmay not be necessary.

It is worth noting that UPS units both condition the power that goesthrough them and, if power is lost, use batteries to deliver backuppower. Their capacity is therefore two-fold: the sustained amperage theycan condition; and how many minutes of power they can deliver at a setload percentage, usually 100% for rating purposes. The amperage capacityis a function of the design of the UPS. The battery capacity is acombination of the amperage capacity and the number of batteries thatare connected to the UPS. The battery capacity can be changed usingexternal battery packs so the battery runtime of the UPS is increased tothe desired target level.

Still another illustrative data center configuration includes twoindependent line power sources from two different power grids. In thisconfiguration, only line power sources are used, but they are deliveredon different distribution legs. This can reduce risk by insuring thattwo power branch distribution circuits must trip their breakers beforepower is lost to the equipment.

Effectively use of the auto-switching of power distribution to the EDPequipment between two independent power sources involves a device thatcan detect power loss (e.g., partial or complete failure of one or morephases of an input power signal) and automatically switch the inputpower to the connected EDP equipment to the other power source. To thisend, some embodiments described herein provide efficient, reliable, andcost-effective automatic transfer switches (ATSs) for use in these typesof EDP equipment deployment scenarios. For at least the reasonsdiscussed above, ATSs (e.g., for single power cord devices) can saveenergy and reduce power costs, while avoiding interruptions in supplypower to the connected EDP equipment.

Various embodiments described herein provide additional features. Someembodiments provide space-efficient parallel ATS deployments in datacenter rack configurations. These embodiments can provide alternatetechniques to maximize the efficiency of usage of data center floorspace and allow the deployment of the maximum number of equipment racksin a data center environment. Other embodiments provide configurationsof ATSs and/or power cords to minimize power cable routing and/orairflow issues in data center equipment racks (e.g., “2-post” and/orcabinet (“4-post”) equipment racks). Still other embodiments incorporatelocking power cord technologies at one or both ends of power cords formore secure power delivery, for example in data centers located inseismically active geographies (e.g., California).

In particular, embodiments combine a number of small ATSs (e.g.,referred to herein as “micro-ATSs”) in parallel with integrated controllogic to construct a large capacity, fast, efficient, and relatively lowcost ATS. Certain embodiments of the micro-ATSs incorporatefunctionality described in PCT Application No. PCT/US2008/057140, U.S.Provisional Patent Application No. 60/897,842, and U.S. patentapplication Ser. No. 12/569,733, all of which are fully incorporatedherein by reference for all purposes. Embodiments of the micro-ATSs willbe discussed below, followed by embodiments for deploying the micro-ATSsto provide redundant power distribution.

Micro-ATS Embodiments

Traditional ATSs tend to have limitations that prevent their effectiveuse in implementations of highly parallel, auto-switched, powerdistribution architectures. For example, these traditional ATSs maytypically be too inefficient, consume too much rack space, and cost toomuch. Embodiments of the micro-ATS described herein address some or allof these issues.

According to one embodiment, the micro-ATS (e.g., the Zonit μATS™) isvery small (e.g., 4.25-inches×1.6-inches×1-inch, or less than 10 cubicinches) and very efficient (e.g., less than 0.2 volts at maximum loadloss). Certain implementations use no rack space, as they areself-mounted on the back of each EDP device, incorporated in thestructure of the rack outside the volume of the rack used to mount EDPequipment, incorporated in rack-mounted plugstrips, or incorporated inan in-rack or near-rack Power Distribution Unit (i.e., any of whichbeing possible due to the small form-factor of the micro-ATS). In otherimplementations, the micro-ATS is small enough to be integrated directlyinto the EDP equipment itself.

Various embodiments of micro-ATSs are described herein, including theirvarious components. For the sake of clarity and context, the micro-ATSembodiments are described as switching between two separate powersources, “A” and “B.” In some implementations, the A and B power sourcesare single-phase sources. In other implementations, polyphase powersources are connected. Where polyphase power sources are connected,polyphase embodiments of micro-ATSs are used. Substantially the samecomponents (e.g., circuits) described herein with reference to thesingle-phase implementations are applicable to the polyphaseimplementations.

For example, polyphase embodiments can be implemented as multiplesingle-phase micro-ATS units acting in parallel, with additionalfunctionality provided for synchronizing certain of the control circuitsso that they act together across the multiple ATS units to handleswitching and return from one polyphase source to the other polyphasesource and back. Various embodiments of polyphase micro-ATSs can alsohave different conditions under which to switch power sources. Forexample, given three phase power with X, Y, and Z “hot” leads, a faulton any of three might be considered reason to switch from the A to the Bpolyphase source. To return to the A polyphase source, it may bedesirable to ensure first that all three hot leads are present, stable,and of sufficient power quality on the A source.

Triac Augmentation of Relay Closure

The following description is one preferred instantiation of the currentdiversion technique described earlier. Although it is described in thecontext of dealing with the issue of relay skew in the parallel modularATS, it should be noted that it can be used in implementations of theZonit Micro Automatic Transfer Switch described herein, for the purposeof building a programmable switching time Zonit Micro Automatic TransferSwitch, that can use that feature. In that instance, relay skew may notbe an issue, but the gain of a programmable switching time that isfaster than a mechanical relay can deliver may be desirable.

Use of a solid state semiconductor switch, preferentially a Triode forAlternating Current switch device, (triac) is identified in thisapplication for the purpose of improving the speed at which a mechanicalrelay can effect the conduction of AC power from the non-conductingstate. The triac is connected in parallel with the contacts of themechanical relay (relay) such that either device, the relay or the triacwill conduct current if it is energized to do so. In this case, thecharacteristic of a mechanical relay that it takes some time, on theorder of many milliseconds, to start conduction current after it hasbeen energized can be temporarily bypassed by the use of a simultaneousconduction of a triac. When the desire to have AC power delivered tosome load via the relay/triac combination is initiated, current canbegin conduction within a very short time of that initiation signal, onthe order of micro-seconds. Upon the relay mechanical contactscompleting the conduction path (closure) the triac is no longerconducting, as it is effectively shorted. The power now passing throughthe relay is efficiently passed with almost no electrical power loss asopposed to the power that momentarily passed through the triac. Duringthe conducting state of the triac, it loses some of the power applied toit because of the characteristic of semiconductors that results inhaving to have a voltage drop across the conduction terminals to allowfor solid state physics to function. This is often known as the “onvoltage”, the lowest voltage that the device can experience between it'sconducting terminals and still have enough energy to sustain the oncondition. In this state, current passing through the device ismultiplied by the on state voltage for a total power dissipation. Thispower dissipation is considered wasted power, as it is not applied tothe load the switch is delivering power to. In a triac, this loss can beon the order of 1 to 2% of the applied total power. Thus, using a triacby itself is inherently inefficient. By only expecting the triac tocarry the power during the short time it takes for the mechanical relayto operate, the power loss is minimized while the time to conductionfrom initiation is minimized.

The simultaneous application of many of these thusly configured hybridtriac/mechanical relays in parallel, in conjunction with a currentsharing pass resistor or high power negative temperature coefficient(NTC) resistor (also referenced herein as an Inrush Limiter) is a uniquecombination with many benefits. The end power control system has thehigh efficiency characteristics of a conventional mechanical relay withthe turn-on speed advantage of a semiconductor device, e.g. triac. Itshould be noted that other semiconductor devices such as BipolarJunction Transistors (BJT), or Metal Oxide Semiconducting Field EffectTransistors (MOSFET), or other fast operating devices can be substitutedfor the triac in applicable variants of this configuration.

The combination of the traditional mechanical relay and the triac isshown in FIG. 32. The relay coil is energized by an incoming signal witha fast rise time, between 1 and 10 microseconds. Energizing the relaywill result in a several millisecond delay before the main contactsclose. At the same time current is applied to the coil, a pulse isgenerated through the capacitor to the pulse transformer as a result ofthe rapid rise time of the incoming signal. The resultant pulse triggersthe triac gate and the triac goes into conduction. It will stay in thisstate until current through the triac is at or very near zero, and thereis no gate current present. At this point, the triac is carrying currentfrom the input of the mechanical relay to the output of the relay andbypassing the contacts of the relay. After some period of time, themechanical components of the relay will move and the mechanical contactswill make electrical connection. The contacts will now carry the currentinstead of the triac. The pulse of the gating signal is designed tooverlap this moment in time by a few milliseconds. This is so when thecontacts bounce, as they will do in any mechanical relay, the conductionpath will be restored through the triac as soon as the mechanicalcontacts open, however momentarily. This will eliminate the electricalinterruption of current flow through the assembly. After some additionalperiod of time, the mechanical contacts cease to bounce and the triac isno longer needed. At this time, the gate current from the pulsetransformer has expired, and the triac is off. When the relay contactsopen next, the electrical connection will be immediately interrupted.Thus, the triac augmentation is designed and intended to augment theperformance of the relay during the energization phase related toclosure of the mechanical contacts only. It has no intended affectduring the opening of the mechanical relay via traditional means.

When the relay does open, a secondary issue arises.

Dv/dt Control in Triac Augmented Relay Closure Application for ParallelRelay Configurations

Current Sharing between relays must be maintained so no one relay takesexcessive current. Each relay must carry less than or equal to it'srated capacity, and no more. When multiple relays are connected in aparallel arrangement as described, that current sharing will beaccomplished as described herein. This method of allowing thetransitional period of the relays to limit the total current through anyone relay also allows for resolution of another problem, the containmentof rate of voltage rise falsely triggering the Triac contact augment.This problem, referred to as the dv/dt limit is, simply stated. that thetriac will self trigger for a half cycle if the rate of rise of thevoltage presented to its main terminals exceeds a certain volts/timethreshold, even when no gate current is present. To overcome thatproblem, one approach is to place an electronic filter in the path ofthe power that limits that rate of rise. However, the components arebulky and add significant costs to the manufacturing of the finishedproduct. Due to the necessity of installation of the current limiting“Inrush Limiter” e.g., negative temperature coefficient resistor, toresolve the transitional current sharing issues, this same component canbe used in conjunction with additional components in the dv/dt controlnetwork to reduce the bulk and cost of that network. This combination ofcomponents is unique.

Details of Operation.

FIG. 32a is a schematic representation of one Alternating Current, [AC]power control relay assembly incorporating the triac augmented relaycontacts and the current sharing and de-skew relay combination. It iscomprised primarily of relay 1 (1) and relay 2 (2) in the current pathwith a triac (8) bypassing the relay 1 (1) contacts. In this figure thepower is not being conducted from the AC input (3) to the AC output (4),it is in the “off” condition. No current is present in the relay coils(1) (2) and neither relay is energized. FIG. 32b represents the initialphase of closing the power path from the AC input (3) to the AC output(4). External logic has determined the need to close the power path andhas applied a voltage to the relay 1 (1) coil (2) via inputs Relaydrive− (7) and Relay drive+ (6). The rise time of the voltage applied isessentially a square wave edge, e.g. fast rise time, on the order of 10to 100 microseconds. Simultaneous to the current being applied to thecoil (2), the fast rise time causes current to flow through Capacitor C1(12), through Diode D1 (13), resistor R1 (14), into the primary windingof pulse transformer 1 (10), and back to the input via Relay drive− (7).This rapid change in voltage across the pulse transformer (10) causes apulse to be generated on the secondary winding of the pulse transformerand appear as a positive going pulse at the gate (5) of the triac (8).In the first few nano-seconds of the pulse, the triac (8) begins to turnon, but as of yet, no current is flowing from the AC input (3) to the ACoutput (4) because the relay (1) is also not yet changed state. In fact,the relay (1) will take a significant amount of time to close theconnection because of the time required for the field to build in thecoil (2) and for the mechanical component that moves, the armature (18)to accelerate, and move through the space between the off position andthe conducting [on] position. This time will take on the order of 5 to20 milliseconds. This instant, the instant the voltage was applied tothe relay control inputs (6) (7), is herein referred to as the “T”moment, and time from this position will be described as T+[time inmicroseconds or milliseconds]. At this time, T+0 microseconds, relay 2(2) also has no current applied to it's coil (1). Thus the relaycontacts are not conducting, and the only current path available pastthe relay contacts will be via the Negative Thermal Coefficient resistor[or “inrush limiter”] NTC 1.

FIG. 32c represents the initial conduction of AC current from the ACinput (3) to the AC output (4) at T+5 milliseconds. This time isdependent on the mechanical characteristics of the relay, and can befrom 3 to 18 milliseconds for many common relay types, but is notrestricted to any specific value. However, due to the mechanical natureof any mechanical relay, the time will be on the order of milliseconds.The triac (8) has become fully conduction, and is passing the currentpast the contacts of the relay 1 (1), and in fact has been doing sosince about T+1 microsecond or so. The armature (18) of relay 1 (1) isshown in transition from the “off” state to the “on” state, and is saidto be “in flight”. Still no current is being passed through the contactsof relay 1 (1), but rather through triac 1 (8), then through the NTC 1(17) and to the AC output (4). Effectively, the triac (8) is carryingthe current to the AC output (4) during the “flight time of the relayarmature (18). The current applied to the AC output (4) is limited bythe NTC 1 (17), and initially, just after the triac (8) starts toconduct for a hundred nanoseconds or so, by choke 1 (9). The need forthis choke will become apparent later, but has little effect at thistime. The NTC 1 starts out with some resistance to flow, on the order ofabout 2 ohms, but because of the current now passing through it, it iswarming up and the resistance is lowering. But because the resistancewas higher moments before when the NTC 1 was cold, the current islimited to a safe value, regardless of the impedance of the load. Thatis to say, if the load is at or near zero ohms, then the voltage appliedresults in the maximum current being limited by ohms law to a manageablecurrent that does not destroy the triac (8), or eventually the relay1(1) when it finally conducts. Even if the output is effectivelyshorted, for a few hundred microseconds or a few milliseconds, the NTC 1(17) will absorb the power generated by the voltage being applied. Thisis the key to de-skewing multiple relays in parallel, and will beexplained later.

FIG. 32d represents the condition of the current path at around T+10milliseconds, again dependent upon the mechanical characteristics of therelay. But FIG. 2 is showing the condition just after the armature (18)of relay 1 (1) has made contact with the current carrying contact andthe relay contacts are now in conduction. Note that still, no currenthas been applied to the coil (19) of relay 2 (2). At the moment that therelay 1 (1) contacts close, all current passes through them rather thanthrough the triac (8). The triac (8) has turned “off” and is now notconducting. Also note that no current is flowing through C1 (12), D1(13), R1 (14) and hence the pulse transformer 1 (10). This is becausethe voltage across Capacitor 1 (12) has fully charged, and thus currentthrough it ceases. One side of the capacitor 1 (12), the Relay 1 drive+(6) side is at the input voltage, and the other side of the capacitor ischarged negatively relative to the Relay 1 drive+ (6) side. The lack ofcurrent flowing through the pulse transformer (10) results in no voltagebeing applied to the gate (5) of the triac (8). Since no gate current ispresent, and no current is flowing in the triac, it will now notconduct, regardless of the state of the relay 1 (1) contacts. In actualdesign practice, a slight overlap of the length of time the pulse ispresent at the gate of the triac, and the contacts of the relay becomingclosed is designed in. This overlap allows the triac to be “on” duringthe time the relay contacts are “bouncing”, and inevitable product ofmechanical contacts. This period of time is on the order of about 100microseconds to a millisecond or so. But the selection of the capacitor1 (12) value can be made to provide current to the gate (5) of the triac(8) for just enough time to cover the “flight time” of the armature(18), and a small amount plus. This is another positive “feature” ofthis design.

FIG. 32e represents the next logical phase in finalizing the currentpath from the AC input (3) to the AC output (4). This phase is necessaryto bypass the NTC 1 (17), since it is now carrying the current, and as aresult is dissipating power. Bypassing this device with and additionalrelay (2) nearly eliminates the power loss in the NTC 1 (17), thusmaking the switch more efficient. De-Skew Relay 1 drive+ (16) andDe-Skew Relay 1 drive− (15) now have a voltage applied and current isgoing through the coil (1) of relay 2 (2).

However, due again to the mechanical nature of the relay, the armature(19) is shown in “flight”, and current is still flowing through the NTC1 (17).

FIG. 32f represents the final conditions of the total assembly in the“on” state, no further changes will occur while the assembly is in thisstate. Coil current is applied to both relay coils (2),(1) and bothrelay armatures (18) (19) are in full conduction. Power is deliveredfrom the AC input (3) to the AC output (4) with minimal loss and powerdissipation.

FIG. 32g represents the initiation of the disconnect sequence where thepower path from the AC input (3) to the AC output (4) is to bediscontinued. The sequence begins by power to Relay 2 (2) coil (1) beingremoved via De-Skew Relay 1 drive+ (16) and De-Skew Relay 1 drive− (15)voltage being removed. A short time after the removal of power thearmature (19) or relay 2 (2) disconnects the power path through therelay. Immediately, current now must travel through the NTC 1 which isnow cold, and at its maximum resistance. This action now limits thetotal current that can pass from the AC input (3) to the AC output(4).). The NTC 1 starts out with some resistance to flow, on the orderof about 2 ohms, but because of the current now passing through it, itis warming up and the resistance is lowering. But because the resistancewas higher moments before when the NTC 1 was cold, the current islimited to a safe value, regardless of the impedance of the load. Thatis to say, if the load is at or near zero ohms, then the voltage appliedresults in the maximum current being limited by ohms law to a manageablecurrent that does not destroy the triac (8), or eventually the relay1(1) when it finally conducts. Even if the output is effectivelyshorted, for a few hundred microseconds or a few milliseconds, the NTC 1(17) will absorb the power generated by the voltage being applied. Thisis the key to de-skewing multiple relays in parallel, and will beexplained later. It also provides a limited current path that iscritical to the subsequent actions in this phase of the disconnectsequence.

FIG. 32h represents the start of the last phase of the disconnectsequence. Power to the relay 1 (1) coil (2) has been removed by thevoltage applied to Relay 1 drive+ (6) And Relay 1 drive− (7) beingremoved and going to zero. Current still passes through the contacts ofrelay 1 (1) via the armature (18), as inertia has not yet allowed it todisconnect. At this point, the magnetic field in the coil (2) is juststarting to collapse, and soon (almost instantly) Electro-Motive-Forcefrom that coil will begin to apply a negative voltage across Relay 1drive+ (6) And Relay 1 drive− (7). But at this instant, when the voltageat Relay 1 drive+ (6) And Relay 1 drive− (7) goes to zero, the chargestored in Capacitor C1 (12) is starting to discharge via resistor R2(31) and Diode D2 (20) to the Relay 1 drive− (7). Since the discharge isgoing negative, no current is conducted through diode D1 (13), resistorR1 (14), and thus no pulse is formed in pulse transformer 1 (10). Thetriac (8) remains “off”. This discharge path is necessary to prepare thetriac gating circuitry for the next turn-on sequence when the next eventoccurs that wishes to again turn “on” the path from the AC input (3) tothe AC output (4). For now, to minimize the time to disconnect the powerpath, the triac (8) must remain non-conducting.

FIG. 32i represents the moment of the disconnection of power from the ACinput (3) to the AC output (4). The armature (18) of relay 1 (1) is now“in flight”. It can take several milliseconds to complete, but thecontacts are now separated, and with the triac (8) in the off state, thevoltage across the contacts of relay 1 (1) rises very fast, depending onthe point in the AC cycle that the disconnection occurs. It must beassumed that this is coincidental with the peak of the AC cycle. Withthe Load impedance of the AC out (4) being very low, perhaps nearly zeroohms if this is the last of multiple relays in parallel to disconnect,the voltage rise across the main terminals of the triac (8) could bevery fast if not controlled. This is the point in the sequence that iscrucial for the intent of this application. The components, Capacitor 2(11), Choke 1 (9), and NTC 1 (17) work together to slow the rate of riseof the voltage across the Main terminals of the triac (8). This actionis necessary since a high rate of voltage application will falselytrigger a triac as previously described. In a conventional applicationof a triac, a so-called “snubber” circuit consisting of a relativelylarge choke and relatively large capacitance in place of the Choke (9)and capacitor C2 (11) would be necessary to manage the extreme currentspossible. But, because the NTC 1 resistor is now in the AC power path,current is limited, and these two components, the choke 1 (9) and thecapacitor c2 (11) can be significantly smaller presenting a significantspace and cost savings. As the voltage starts to rise at the junction ofchoke 1 (9) and NTC 1 (17), It can do so for the first few micro-secondswith little effect at the junction of capacitor 2 (11) and choke 1 (9).This is due to the inductance of choke 1 (9). Since the voltage can bechanged across it rapidly with no current changing, the current into C2(11) is limited. Thus, C2 (11) charges slowly, thus limiting the rate ofrise across the main terminals of the triac (8). But the time constantof the combination of components would have to be extended for the worstcase design requirements of the selected triac. If the NTC 1 were notpresent, the values for the capacitor C2 (11) and the choke 1 (9) wouldhave to be much larger. But because the NTC 1 (17) is still cold, andit's resistance is still relatively high, the rate of rise of voltageacross capacitor C2 (11) continues to be restricted even after thesmaller value choke has saturated and current is going through it. Withproper selection of values for C2 (11), NTC 1, and the triac (8), it maybe possible to even eliminate the choke (9). This would otherwise beimpossible without the unique combination of components that include thede-skewing relay, Relay 2 (2), the NTC 1 (17) and a traditional triacswitch. The unique combination of the triac-augmented mechanical relayof Relay 1 (1) and it's associated components, with the de-skewingcurrent control relay and NTC resistor allows minimizing the componentvalues, cost and possibly eliminating one traditionally required part.

FIG. 32j shows the sub-assembly again at quiescent state ofnon-conduction from the AC input (3) to the AC output (4). Capacitor C1(12) is fully discharged.

FIG. 32K represents a set of three of the base relay assembliesdescribed previously. The array can be any number of relay assembliesfrom 2 to N, where N is the number of relays necessary to achieve thedesired total power handling capability. If the individual relay modulesare 50 Ampere modules, for example, a 4000 Amp capable assembly wouldrequire 80 individual relay modules connected together as shown, inparallel. It should be noted that individual relay coils can becontrolled in parallel groups as shown on the De-Skew Relay Drive relays2, 4, and 6 (2) (4) (6) from a single driver, or configuredindependently as shown on the Relay 1, Relay 3, and Relay 5 (1) (3) (5).When connected in parallel, the drive circuitry is simpler and easier tomake highly reliable. When connected independently to individualdrivers, the relays can have dynamically controlled input timingallowing fine precision in adjusting the time of actuation and time ofrelease. The advantage of such added complexity is the ability torecursively adjust the actuation and de-actuation of the relays tosynchronize the contacts actual landing and disconnection of the mainpower path for the purpose of minimizing the duration that any one relayshould take either more or less than the average current of the parallelgroup.

In this figure, the NTC 1 is the current limiter for whichever relaytends to be first to close and last to open. These two conditions arethe extreme load case for the relays and other power path components.With 2 ohm value NTC 1 components, the current in any one given path islimited to 120 Amps for a 240V switch. Each of the components can bespecified to withstand that 120 Amps for the duration necessary to haveenough of the relay sub-assemblies become parallel connected ordisconnected, whichever event is occurring. Thus, utilizing a resistor,or NTC resistors (17) (35) (55) in each of the outputs of a sub-module anecessity, it enables the use of fewer and/or lower cost components inthe snubber network for the triac, and even is advantageous tooptimizing the size and power handling capability of the triac.

Embodiments Using Micro-ATSs for Redundant Power Distribution

ATSs can be deployed at various points in the power distributiontopology to provide for automatic failover from a primary power sourceto a backup power source typically at one of three points in the powerdistribution topology: the panelboard on the wall, where the branchcircuits originate; the end of the branch circuit in the rack where thepower is fed to plugstrips; or between the plugstrip and the EDPequipment being powered. The choice of where to place auto-switchingfunctionality in a power distribution topology can involve considerationof a number of issues.

One issue to consider when determining where to place auto-switchingfunctionality in a power distribution topology is the potential domainof failure, the number of power receptacles that will be affected if anATS fails to function properly. Power distribution topologies used indata centers can be considered rooted tree graphs (i.e., mathematicallyspeaking), so that the closer to the root of the tree the ATS islocated, the higher the number of power receptacles that will beaffected by the actions of that ATS. For example, FIGS. 18A-18D showillustrative power distribution topologies.

Turning to FIG. 18A, a power distribution topology 1800 a is shownhaving an ATS 1840 a disposed in the root nodes 1830 of the topology.For the sake of clarity, the power distribution topology 1800 a includesa core infrastructure 1810, root nodes 1830, distribution nodes 1850,and leaf nodes 1870. The root nodes 1830 is considered to be“downstream” of the core infrastructure 1810. Each portion of the powerdistribution topology 1800 a includes power distribution components.

As shown, the utility grid 1805 feeds a site transformer 1815 in thecore infrastructure 1810 (e.g., a step down transformer). The coreinfrastructure 1810 also includes a local generator 1820. The sitetransformer 1815 and the local generator 1820 act as two independentsources of power for the power distribution topology 1800 a. In otherembodiments, other independent sources, such as independent utilitygrids, and/or more than two independent sources may be used. In someimplementations, main switch gear 1825 can allow the entire coreinfrastructure 1810 to be switched to alternate power (e.g., from thesite transformer 1815 to the local generator 1820).

Power is provided from the core infrastructure 1810 to the root nodes1830 of the power distribution topology 1800 a. In the illustrativepower distribution topology 1800 a of FIG. 18A, the root nodes 1830include one or more uninterruptable power supplies (UPSs) 1835. Itshould be noted that large data centers often have many generators andUPSs 1835, since there is a limit to the capacity size you can buy, andif you exceed that limit, you have to install multiple UPSs 1835 and runthem in parallel. Each UPS 1835 can be considered as a root node 1830 inthe power distribution topology 1800 a.

Power paths coming from the main switch gear 1825 and the UPS(s) 1835are routed to an ATS 1840 a disposed as a root node 1830. The ATS 1840 ais configured to automatically switch between core power coming from thecore infrastructure 1810 and power coming from the UPS(s) 1835 (e.g., incase of a full or partial power failure in the core infrastructure 1810.In this way, the ATS 1840 a provides reliable, constant power todownstream components.

As illustrated, power is delivered from the root nodes 1830 to thedistribution nodes 1850. In particular, the output power from the ATS1840 a is delivered to one or more panelboards 1855. In someimplementations, multiple power distribution panelboards 1855 are used,since they come only so large in power capacity and number of circuitbreaker stations. Also, it may be more efficient to locate panelboards1855 so as to minimize the average power whip length, and as many as ispractical may be used to accomplish this purpose. It should be noted,that busways can be used with or instead of panelboards in the powerdistribution topologies described herein.

Typically, the distribution nodes 1850 are considered as originating atthe main panelboards 1855 and ending at equipment racks 1875 (e.g., leafnodes 1870). In the illustrative embodiment, power is distributed at theequipment racks 1875 via plugstrips 1880. The plugstrips may also havecircuit breakers in them. It is worth noting that some of skill in theart confusingly refer to both panelboards 1855 and plugstrips 1880 aspower distribution units (PDUs). Accordingly, for the sake of clarity,the terms panelboards and plugstrips are used herein.

The equipment racks 1875 include EDP equipment 1885. Many types of EDPequipment 1885 are possible, and may be rack-mounted in the equipmentracks 1875. Each piece of EDP equipment 1885 can be plugged into one orboth plugstrips 1880. For example, EDP equipment 1885 having multipleinternal power supplies may be plugged into multiple plugstrips 1880

In the illustrated configuration, the ATS 1840 a is deployed as a rootnode 1830 of the power distribution topology 1800 a, upstream of thedistribution nodes 1850 and leaf nodes 1870. This upstream placement mayprovide ATS functionality with only a single (or relatively few) ATSs.Notably, an important factor to consider when determining where to placeauto-switching functionality in a power distribution topology is powerdistribution efficiency—the amount of power that is “lost” by theinsertion of ATSs into the power distribution system. No ATS is 100%efficient (i.e., they all have a loss factor). Generally, it is helpfulto categorize two types of ATSs as relay-based and solid state-based.Each has different characteristics with regards to power loss andtransfer time. In many applications, transfer time between the powersources is important, because the power supplies used in modern EDPequipment can often only tolerate very brief power interruptions. Forexample, the Computer and Business Equipment Manufacturers Association(CBEMA) guidelines used in power supply design recommend a maximumoutage of 20 milliseconds or less.

Mechanical relay-based ATSs use one or more mechanical relays to switchbetween their input power sources. Generally speaking, relays have twoprimary loss factors, the contact area of the relay, and any power therelay may require to maintain it in the “ON” state (i.e., in which it isconducting current). The shape and material of the contacts is carefullychosen and engineered to minimize resistance across the contacts, yetminimize or prevent arcing across the contacts when they are switching.Also, since some arcing may occur in some circumstances, the contactsmust be designed to minimize the possibility of the arc “welding” thecontacts shut, which can be highly undesirable.

Another design issue is transfer time of the relay. The contacts aremounted (e.g., on an armature) so that they can be moved to accomplishtheir switching function. The contact mass, range of motion, mechanicalleverage, and force used to move the armature are all relay designissues. The range of motion is dictated by the gap needed between thecontacts to minimize arcing at the maximum design current level. As themaximum design current is increased, the gap also tends to increase. Themass of the contact is accelerated by the force applied to the armature,which has a practical limit.

These factors can impose a limit on the amount of current that can besent through a pair of contacts and still maintain an acceptabletransfer time for EDP equipment. For example, if the mass of thearmature and contact gap are too large, the relay transfer time canexceed a threshold time limit (e.g., the CBEMA recommend maximum ofapproximately 20 milliseconds of power outage for continued operation ofmodern switched power supplies). Well designed relay-based ATSstypically manifest a loss factor of about 0.5% or less. They also havepower supplies to power their internal logic that typically use in therange of 12-20 watts in operation.

In the case of solid state-based ATSs, the switches use solid statesemiconductors to accomplish switching between their input power sourcesand their output load. They can typically switch faster than comparablerelay-based switches, because they use semiconductor-based switchingrather than mechanical relays. However, the semiconductors also have aloss factor, and the efficiency of this type of switch is often lessthan that of a relay based switch (e.g., around 1%). Also, they areoften less reliable, unless they are built with redundant internalfailover capability, which can make them appreciably more expensive. Aswith their relay-based counterparts, solid state-based ATSs typicallyhave power supplies to power their internal logic that use in the rangeof 12-200 watts

or more in operation, depending on the size of the transfer switch, andthe level of redundancy offered by the switch.

It should be noted that the ATSs that are upstream of the UPS units areconsidered part of the “core power” infrastructure not the “powerdistribution” infrastructure. Automatic transfer switching can be donein the core infrastructure 1810 to insure continuity of connection to avalid power source, such as utility power grid feeds or generators. Thetransfer time of relay-based switches that can handle the powercapacities required in the core infrastructure 1810 is typically tooslow to avoid shutdown by connected EDP equipment 1885 for the reasonsdescribed earlier (e.g., according to the CBEMA guidelines).Accordingly, ATSs of this type tend to be placed upstream of UPS units,where brief power outages that these switches create on transfer can becovered by the UPS units.

Indeed, large state transfer switches can be used in the coreinfrastructure, as they are fast enough to switch within typical (e.g.,CBEMA) guidelines. However, these types of ATSs are very expensive andcan represent a single point of failure. Further, they tend to have anunfavorable loss associated with power flowing through the semiconductordevices.

As illustrated, the single ATS 1840 a will switch every branch circuitin a given panelboard 1855 to a secondary power source when the primarypower source fails. For at least the above reasons, this type ofupstream placement of the ATS 1840 a in the power distribution topology1800 a can mitigate certain issues (e.g., power loss, transfer time,etc.) that can be exacerbated when many ATSs must be used throughout apower distribution topology 1800 a. However, in this configuration,failure of the single ATS 1840 a upstream of the panelboard 1855 cancause many downstream EDP devices to be deprived of power. For example,a typical panelboard has a capacity of 225 KVA, and 84 or 96 circuitbreaker stations. This can power approximately up to 40 racks via 28-96branch circuits (e.g., depending on the type and number of branchcircuits and the average number of watts used per rack). Having 40 racksbe deprived of power due to a single ATS failure in a data center is amajor hit that can have very serious service impacts. Note: The modularparallel ATS described herein can be used in this location 1840 a. It'sparallel fault-tolerant architecture allows it to deliver sufficientreliability to work well in this role. The higher levels of parallelismdescribed for auto-switching at lower levels of the power topology beloware potentially even more reliable, but the parallel modular ATS hasother benefits that may be desirable.

FIG. 18B shows another illustrative a power distribution topology 1800 bhaving an ATS 1840 b disposed further downstream, in the distributionnodes 1850 of the topology. For the sake of clarity, the powerdistribution topology 1800 b is illustrated as having the same coreinfrastructure 1810 and similar root nodes 1830, distribution nodes1850, and leaf nodes 1870 as those shown in FIG. 18A. Unlike in FIG.18A, the ATS 1840 b is implemented in the distribution nodes 1850.Instead of the main switch gear 1825 and the UPS(s) 1835 feeding an ATSin the root nodes 1830 of the topology, the alternate power paths feeddistribution nodes 1850.

As illustrated, the distribution nodes 1850 include one or more mainpanelboards 1855 a and one or more zone panelboards 1855 b. Some or allof the zone panelboards 1855 b include an integrated ATS 1840 b (ormultiple integrated ATSs 1840 b). The alternate power sources (e.g.,from the main switch gear 1825 and the UPS(s) 1835) feed the integratedATS(s) 1840 b. The zone panelboards 1855 b can then supply power toequipment racks 1875 in their respective zones.

In the illustrative power distribution topology 1800 b, there are stillrelatively few ATSs, which can still reduce issues associated with ATSinefficiencies, etc. However, placing the ATSs 1840 b further downstreamallows the ATSs 1840 b to handle power transfer only for a subset of theequipment racks 1875 in a large data center (i.e., a particular zone).Accordingly, failure of an ATS 1840 b will cause a more limited numberof downstream EDP devices to be deprived of power. This can have a lesscatastrophic impact to the data center than from a similar failure witha farther upstream ATS. The modular parallel ATS described herein can beused in this location 1840 b. It's parallel fault-tolerant architectureallows it to deliver sufficient reliability to work well in this role.The higher levels of parallelism described for auto-switching at lowerlevels of the power topology below are potentially even more reliable,but the parallel modular ATS has other benefits that may be desirable.

FIG. 18C shows yet another illustrative a power distribution topology1800 c having an ATS 1840 c disposed even further downstream, in theleaf nodes 1870 of the topology. For the sake of clarity, the powerdistribution topology 1800 c is illustrated as having the same coreinfrastructure 1810 and similar root nodes 1830, distribution nodes1850, and leaf nodes 1870 as those shown in FIGS. 18A and 18B. Unlike inFIG. 7, the ATS 1840 c is implemented at or near the equipment racks1875 in the leaf nodes 1870.

As illustrated, the main switch gear 1825 and the UPS(s) 1835 feeddistribution nodes 1850 (e.g., main and/or zone panelboards 1855). Thedistribution nodes 1850 in turn feed the leaf nodes 1870. For example,panelboards 1855 supply power to equipment racks 1875. In theillustrative power distribution topology 1800 c, an ATS 1840 c isdisposed at or near each equipment rack 1875 or set of equipment racks1875. In one embodiment, the ATS 1840 c is configured to fit within arack space, as discussed more fully below. In other embodiments, theATSs 1840 c are place on top of equipment racks 1875, next to equipmentracks 1875, or in any other useful location.

In some implementations, the primary power path is distributed from thepanelboard 1855 to a first plugstrip 1880 a of the equipment rack 1875.A second plugstrip 1880 b of the equipment rack 1875 is feds by the ATS1840 c, which is configured to switch between the primary and secondarypower sources, as needed. For example, EDP equipment 1885 having only asingle plug can be plugged into the second plugstrip 1880 b and poweredby the primary power source if of sufficient quality, or otherwise bythe secondary power source. In some implementations, other EDP equipment1885 (e.g., having multiple internal power supplies, two plugs, etc.) isplugged into both plugstrips 1880.

In this configuration, a single ATS failure would only impact thosepieces of EDP equipment 1885 relying on the ATS's switching capabilities(i.e., likely to be only one or a small number of racks' worth of EDPequipment 1885). However, it is worth noting that many more ATSs wouldlikely be used than in the configurations illustrated in FIG. 18A or18B. Further, deployment of the ATSs at the equipment racks 1875 canimpact valuable rack space. The modular parallel ATS described hereincan be used in this location 1840 c. Its parallel fault-tolerantarchitecture allows it to deliver sufficient reliability to work well inthis role. The higher levels of parallelism described for auto-switchingat lower levels of the power topology below are potentially even morereliable, but the parallel modular ATS has other benefits that may bedesirable.

Rack space in a data center can be very expensive. The data centerinfrastructure of generators, UPS units, power distribution, raisedfloor, computer room cooling, raised floors, etc. is often a very largecapital investment and a large ongoing operational expense. One standardrack unit (“1 U”) of rack space in a standard forty-two-unit (“42 U”)equipment cabinet is equivalent to 2.5% of the space available in thatrack. Thus installing rack-mounted ATSs in large numbers in equipmentracks uses a lot of rack space, which represents a loss of space thatcan be used for EDP equipment and would therefore be undesirable.Accordingly, ATSs are often not deployed in that configuration,especially if other options are available.

FIG. 18D shows still another illustrative a power distribution topology1800 d having ATSs 1840 d disposed still further downstream at the EDPequipment 1885, in the end leaf nodes 1870 of the topology. For the sakeof clarity, the power distribution topology 1800 d is illustrated ashaving the same core infrastructure 1810 and similar root nodes 1830,distribution nodes 1850, and leaf nodes 1870 as those shown in FIGS.18A-18C.

As in FIG. 18C, the main switch gear 1825 and the UPS(s) 1835 feeddistribution nodes 1850 (e.g., main and/or zone panelboards 1855), whichfeed the leaf nodes 1870. For example, panelboards 1855 supply power toequipment racks 1875. In the illustrative power distribution topology1800 d, an ATS 1840 d is disposed in, at, or near each piece of EDPequipment 1885 (or at least those pieces of EDP equipment 1885 for whichthe ATS functionality is desired). In one embodiment, the ATS 1840 d isconfigured so that a number of ATSs 1840 d can be combined to fit withina rack space and to run in parallel for a number of connected pieces ofEDP equipment 1885, as discussed more fully below. For example, the ATSs1840 d may be the micro ATSs 700 described above, and may be deployed inparallel with integrated control logic to construct a large capacity,fast, efficient, and relatively low cost ATS for use in providingredundant power distribution for EDP equipment 1885. In otherembodiments, the ATSs 1840 d are integrated into power cords, intopieces of EDP equipment 1885, or disposed in any other useful way.

In this configuration, a single ATS failure would only impact the EDPequipment 1885 it serves (i.e., likely to be only one EDP device).However, this configuration could involve deployment of many more ATSsthan in any of the other configurations illustrated in FIGS. 18A-18C.Each ATS can add inefficiencies in power distribution (e.g., powerloss), space usage (e.g., by taking up valuable rack space), etc.

As discussed above, embodiments include a micro-ATS 700 (e.g., acting asany of ATS 1840 b-ATS 1840 d) that can be deployed in configurationswhere size and efficiency are of concern. For example, the Zonit μATS™is very small (e.g., 4.25-inches×1.6-inches×1-inch, or less than 10cubic inches) and very efficient (e.g., less than 0.2 volts at maximumload loss). Certain implementations use no rack space, as they areself-mounted on the back of each piece of EDP equipment 1885,incorporated in the structure of the equipment rack 1875 outside thevolume of the equipment rack 1875 used to mount EDP equipment 1885,incorporated in rack-mounted plugstrips 1880, or incorporated in anin-rack or near-rack panelboards 1855 (i.e., any of which being possibledue to the small form-factor of the micro-ATS). In otherimplementations, the micro-ATS 700 is small enough to be integrateddirectly into the EDP equipment 1885 itself.

The small form factor of the micro-ATS 700 can enable usage of 24-inchoutside-to-outside width EDP equipment racks 1875. These types ofequipment racks 1875 can provide certain advantages. For example, thecabinets fit exactly on two-foot by two-foot raised floor tiles, whichmakes putting in perforated floor tiles to direct air flows easy, sincethe racks align on the floor tile grid. Further, the equipment racks1875 can save precious data center floor space. NEMA equipment racks1875 are not typically standardized for overall rack width, and thenarrower the rack is, the more racks can be fit in a given row length.For example a 24-inch equipment rack 1875 will save three inches overthe very common 27-inch width equipment racks 1875, thereby allowing forone extra equipment rack 1875 for each eight equipment racks 1875 in arow (i.e., nine 24-inch equipment racks 1875 can be fit into the floorspace of eight 27-inch equipment racks 1875). Narrower equipment racks1875 are becoming more practical with modern EDP equipment 1885, forexample, since almost all models now utilize front to back airflowcooling (i.e., as opposed to side-to-side cooling, which used to becommon, but has now almost completely disappeared). Notably, however, a24-inch equipment rack 1875 has appreciably less space on the sides forancillary equipment like vertical plugstrips 1880, ATSs, etc., such thatthose components must have as small a form-factor as is practical to fitinto the equipment racks 1875.

The micro-ATS 700 allows efficient, cost-effective and rack space savingper device or near per device (ratios of one micro-ATS 700 per one pieceof (or a low integer number of) EDP equipment 1885) and allows highlyparallel and highly efficient auto-switched power distribution methodsto be utilized. It should be pointed out that the ratio of micro-ATS 700units to EDP equipment 1885 can be selected to optimize severalinterrelated design constraints, reliability, cost and ease of movingthe EDP equipment 1885 in the data center. The one-to-one ratiomaximizes per-device power reliability and ease of moving the devicewhile keeping it powered up. For example, this can be performed using adevice-level ATS, like the micro-ATS 700, by doing a “hot walk,” inwhich the device is moved by first unplugging one ATS power cord, movingthe plug to a new location, unplugging the second ATS power cord, etc.Long extension cords make “hot walks” easier. Ethernet cables can beunplugged and reinserted without taking a modern operating system downand TCP/IP connections will recover when this is done. In someimplementations, cost can be reduced by using ratios other thanone-to-one for micro-ATS 700 units to pieces of EDP equipment 1885. Alimiting factor can be micro-ATS 700 power capacity and what raisedlevel of risk the data center manager is willing to take, since the moredevices connected to any ATS the greater the impact if it fails tofunction properly.

Turning to FIG. 19, an illustrative traditional power distributiontopology is shown, according to some prior art embodiments. Asillustrated, the topology includes a “double conversion” technique usingUPS units (e.g., 1835), which in some recent implementations includeflywheel UPS devices. Even some of the best double conversion UPS unitsused in data centers have power efficiencies that vary as their loadchanges.

For example, FIG. 20 illustrates an efficiency versus load graph for atypical double-conversion UPS unit. For example, standard UPS units maytypically average 85-90% efficiency, and flywheel UPS units may averagearound 94% efficiency at typical load levels. This level of efficiencymay be unacceptable in many instances, for example, when power costs arestable and relatively low, and when climate impacts of carbon-basedfuels are appreciated. Recently, power has quickly changed from aninexpensive commodity to an expensive buy that has substantial economicand environmental costs and key implications for national economies andnational security. A traditional UPS powered data center more typicallyhas efficiencies in the 88-92% range, for example, because data centermanagers tend to run UPS units at less than 100% capacity to account forany needed equipment adds, moves, or changes. Also, often the loadbetween the UPS units is divided so that each has approximately ½ theload of the total data center. In this case, neither UPS can be loadedabove 50%, since to be redundant, either UPS must be able to take thefull load if the other UPS fails. This pushes the UPS efficiency evenlower, since each unit will usually not be loaded up above 40-45% sothat the data center manager has some available UPS power capacity foradds, moves, or changes of EDP equipment in the data center.

It is worth noting that the number of very large data centers that houseextremely high numbers of servers has been increasing, such that serverdeployment numbers are extremely high. There are a number of commercialorganizations today that have in excess of one million servers deployed.With facilities of this scale and the increasing long-term cost ofpower, making investments in maximizing power usage efficiency can makegood sense, economically, environmentally and in terms of nationalsecurity.

As discussed above, there are several reasons to put multiple (e.g.,dual or N+1 are the most common configurations) power supplies into EDPequipment 1885. One reason is to eliminate a single point of failurethrough redundancy. However, modern power supplies are very reliable,having a typical Mean Time Between Failure (MTBF) value of about 100,000hours (i.e., 11.2 years), which may be well beyond the service life ofmost EDP equipment 1885. Another reason that multiple power supplies areused is to allow connection to more than one branch circuit. Asdiscussed above, the branch circuit tends to be the most common point offailure for power distribution. Yet another reason is that having dualpower connections makes power system maintenance much easier, forexample, by allowing one power source to be shut down without affectingend user EDP equipment 1885.

However, putting multiple power supplies in EDP equipment 1885 can havevarious costs. One cost arises from the purchase of the additional powersupply(s). For example, the supplies are often specific to eachgeneration of equipment, and therefore must be replaced in each newgeneration of equipment, which can be as short as three years in someorganizations for typical servers.

Further, servers are currently most cost-effective when bought in the“pizza box” form factor. For example, servers deployed in large datacenters are typically all “commodity” Intel X86 architecture compatiblecentral processing units (CPU's). These servers are used to power mostof the large server farms running large websites, cloud computingrunning VMWare or other virtualized solutions, high performancecomputing (HPC) environments, etc. Commodity servers have great pressureto be cost competitive, especially as regards their initial purchaseprice. This in turn can influence the manufacturers' product managers tochoose the lowest cost power supply solutions, potentially at theexpense of yielding the best power efficiency.

Another cost of additional power supplies is that each power supply hasan associated loss factor. For example, power supplies are not 100%efficient and costs can be reduced by designing the supplies to run mostefficiently at a given load range (e.g., typically +/−20% of the optimumexpected load). Many power supplies have an efficiency curve thatresembles that shown in FIG. 20. Notably, a product manager for a servermanufacturer may desire to sell a server in two configurations, with oneor two power supplies, and may prefer to stock only a single powersupply model to avoid additional costs due to stocking, selling, andservicing two models of power supplies. This can trade capital expense(the server manufacturer can sell the server at a lower initial pricepoint) for operational expense. For example, with two AC-to-DC powersupplies, the DC output bus will typically be a common shared passivebus in the class of commodity server that is most often used in largescale deployments. Adding power source switching to this class of serverto gain back efficiency (e.g., when only one power supply at a timetakes the load) may be too expensive for the market being served and canadd another potential point of failure for which additional costs may beincurred to add redundancy for greater reliability.

Further, typical modern EDP power supplies are almost all auto-ranging(i.e., they accept 110-240V input) and all switched (i.e., they draw onthe AC input power for just a short period of time, convert that energyto DC, then repeat). Power supplies of this type can be more resistantto power quality problems, because they only need to “drink” one gulp ata time, not continuously. If the input AC power voltage range iscontrolled within a known range, they will typically function veryreliably. While the power supplies may require sufficient energy in each“gulp” and that the input power is within the limits of their voltagerange tolerance, they may not require perfect input AC waveforms to workwell. This can make it possible to use a data center power distributionsystem that is much more efficient than a fully UPS-supplied powersystem at a very reasonable capital expense.

Embodiments address efficient power distribution (e.g., in data centers)using highly parallel automatic transfer switching. As discussed above,a primary source of loss in traditional data center power systems is theUPS unit(s) (e.g., due to conversion losses). One technique for avoidingthese losses is to use filtered utility line power, though this canbring a set of issues that need to be solved before the methodology canbe practical.

FIG. 21 shows an illustrative power distribution topology 2100,according to various embodiments. As described above, the powerdistribution topology 2100 can be considered as having a coreinfrastructure, which can include a site transformer 1815 (e.g., a stepdown transformer fed by the utility grid 1805), a local generator 1820,and a main switch gear 1825. The site transformer 1815 and the localgenerator 1820 act as two independent sources of power for the powerdistribution topology 2100. In some implementations, main switch gear1825 can allow the entire core infrastructure to be switched toalternate power (e.g., from the site transformer 1815 to the localgenerator 1820).

Power is provided from the core infrastructure to the root nodes of thepower distribution topology 2100. As illustrated, core power isdelivered from the main switch gear 1825 to one or more UPSs 1835 and aTransient Voltage Surge Suppression (TVSS) unit 2110. The TVSS acts as avery efficient (e.g., often above 99.9%) and mature technology forfiltering input power to the distribution nodes of the topology. Bycontrast, UPSs 1835 may typically be between 85% and 94% efficient (orless).

In this configuration, the root nodes of the power distribution topology2100 effectively deliver an efficient, primary (“A”) power source 760and a less efficient, secondary (“B”) power source 765. Each of thesepower sources is then routed through the distribution nodes of the powerdistribution topology 2100. For example, one or more panelboards 1855(e.g., main and/or zone panelboards 1855) are used to distribute “A”power 760 and “B” power 765 to the equipment racks 1875 at the leafnodes of the power distribution topology 2100.

In some implementations, the panelboards 1855 deliver power toreceptacles 2125 (e.g., standard 120-volt NEMA receptacles). Eachequipment rack 1875 includes at least a first plugstrip 1880 a having aplug 2120 configured to plug into a receptacle 2125 supplying “A” power760, and a second plugstrip 1880 b having a plug 2120 configured to pluginto a receptacle 2125 supplying “B” power 765. Accordingly, both “A”power 760 and “B” power 765 are delivered by the power distributiontopology 2100 all the way to the equipment racks 1875 in which the EDPequipment 1885 is installed.

Each piece of EDP equipment 1885 for which ATS functionality is desiredcan be supplied with redundant power (i.e., both “A” power 760 and “B”power 765) through the plugstrips 1880 by exploiting micro-ATS 700functionality. As illustrated, micro-ATSs 700 are electrically coupledwith (e.g., plugged into) “A” power 760 and “B” power 765 (e.g., via thefirst and second plugstrips 1880, respectively), and are electricallycoupled with one or more pieces (e.g., typically one or a small number)of EDP equipment 1885. According to a typical operational profile, themicro ATSs 700 are configured to deliver “A” power 760 to the EDPequipment 1885 with it is of sufficient quality and to switch over to“B” power 765 when a partial or complete power failure is detected on“A” power 760.

Some additional features can be realized by deploying multiplemicro-ATSs 700 in a highly parallel fashion as a module. FIGS. 22A and22B show illustrative parallel micro-ATS modules 2200, according tovarious embodiments. According to some implementations, the parallelmicro-ATS modules 2200 are configured to fit within a single rack space(“1 U”). A rack-mountable enclosure 2205 contains two or more micro-ATSs700 (e.g., twelve) configured to operate in a parallel fashion.

As illustrated, the parallel micro-ATS modules 2200 connect to “A” power760 and “B” power 765 (e.g., via an “A” power cord 2210 a and a “B”power cord 2210 b, respectively). The amperage of the “A” and “B” powersources can be chosen to match the number of auto-switched outputreceptacles (described below) and their anticipated average and/ormaximum power draw. The parallel micro-ATS modules 2200 takes inputpower from “A” power 760 and “B” power 765 and distributes to itscomponent micro-ATSs 700. The “A” and “B” power sources may be singlephase, split-phase or three-phase, though they may typically besubstantially identical.

Each component micro-ATSs 700 feeds an output receptacle (ATS receptacle2225 of FIG. 22A) or a hard-wired power cord (output cord 2235 of FIG.22B). In some embodiments, the ATS receptacle 2225 or output cord 2235is accessible via the face (e.g., rear face) of the enclosure 2205 forconnection with EDP equipment 1885 in the equipment rack 1875. Certainembodiments also include one or more ATS indicators 2230 that canindicate, for example, whether a particular micro-ATS 700 is functioningproperly, which power source is currently being supplied, etc. In someembodiments, the parallel micro-ATS modules 2200 include circuitbreakers 2215, optionally with visual power status indicators 2220, toallow disconnecting the parallel micro-ATS modules 2200 electricallyfrom the branch circuits that feed it (i.e., from “A” power 760 and/orfrom “B” power 765).

As illustrated, some embodiments also include a control module 2250 toprovide control functionality for improved parallel operation of thecomponent micro-ATSs 700 in the parallel micro-ATS modules 2200.According to certain embodiments, the control module 2250 helpsparallelize operation of the multiple component micro-ATSs 700. In otherembodiments, the control module 2250 offloads certain functionality ofthe component micro-ATSs 700. For example, in some implementations, theparallel micro-ATS module 2200 is designed to switch all its micro-ATSs700 upon detection of the same condition (e.g., a particular thresholdreduction in power quality). In these types of configurations, certainimplementations move functionality of the detection components (e.g.,one or more of the “A” power voltage range detect subsystem 710, “A”power loss detect subsystem 715, output current detect subsystem 740,etc.) to the control module 2250. When the control module 2250 detects apower failure in the “A” power 760 source, for example, it may force allthe component micro-ATSs 700 in the parallel micro-ATS module 2200 toswitch their outputs to “B” power 765.

Embodiments of the parallel micro-ATS modules 2200 are configured sothat the enclosure 2205 can be mounted within the equipment rack 1875,on top of the equipment rack 1875, or the side of the equipment rack1875. The size of the enclosure 2205 can be minimized due to the verysmall form factor of component micro-ATSs 700. Some implementations ofthe enclosure 2205 are configured to have dimensions within one NEMAstandard rack unit (e.g., 1.75-inches in height). For example,embodiments of the micro-ATSs 700 have dimensions of 4.25 inches deep by1.6 inches high by one inch wide, so that twelve or more micro-ATSs 700can easily fit within a parallel micro-ATS modules 2200, along with anycabling, control circuitry, buses, cooling, etc.

FIG. 23 shows an illustrative power distribution topology that includesa rack-mounted parallel micro-ATS module 2200, according to variousembodiments. Though not shown, it is assumed that a core infrastructureis used to provide at least two independent sources of power. The powersources can be delivered through one or more root nodes to one or moredistribution nodes. As illustrated, root nodes of the power distributiontopology 2300 effectively deliver a primary (“A”) power source 760 and asecondary (“B”) power source 765 through one or more panelboards 1855.

In some implementations, the panelboards 1855 deliver power toreceptacles 2125 (e.g., standard 120-volt NEMA receptacles). Eachequipment rack 1875 includes a parallel micro-ATS modules 2200 that canconnect with the “A” power 760 and the “B” power 765 sources using inputpower cords 2210 (e.g., via respective plugs 2120 configured to pluginto respective receptacles 2125). Accordingly, both “A” power 760 and“B” power 765 are delivered by the power distribution topology 2300 allthe way to the equipment racks 1875 in which the EDP equipment 1885 isinstalled via the parallel micro-ATS modules 2200.

Each piece of EDP equipment 1885 for which ATS functionality is desiredcan be supplied with redundant power (i.e., both “A” power 760 and “B”power 765) by being connected to a component micro-ATS 700 of theparallel micro-ATS module 2200. For example, as discussed above, theconnection to the parallel micro-ATS module 2200 may be implementedusing a receptacle (e.g., ATS receptacle 2225 of FIG. 22A) or an outputpower cord (e.g., output cord 2235 of FIG. 22B). The illustratedembodiment shows cords 2305 connecting the parallel micro-ATS module2200 with each piece of EDP equipment 1885.

According to various embodiments, “hydra” power cords are included. Forexample, the cords 2305 may be combined into a single hydra cord tofurther allow the dimensions of the equipment rack 1875 to be optimizedto most efficiently use data center floor space and to allow the maximumnumber of racks to be deployed in a given area of floor space. Hydracords can be optimized to increase power efficiency delivery, cordrouting, eliminate cord tangle, and incorporate locking power cordfunctionality. In some embodiments, the hydra power cords are connectedto the parallel auto-switch module via standard receptacles, locking ornon-locking or directly attached via hard-wire. In environments wherethe contents of the equipment rack are pre-designed, the hydra cords canbe used as a wiring harness for the “programmed deployment.”

The number of heads on the hydra cord can be varied to match the desiredaverage power output to each connected end-user device. The length andgauge of the hydra power cord (both the main feed section and theseparate feeds to each “hydra head”) can be optimized to minimizeelectrical transmission losses and power cord tangle by optimizing thecord lengths for each hydra cord to supply power to a particular set ofequipment positions in the equipment rack 1875. A set of appropriatelysized hydra cables can be used to feed each equipment location in therack at whatever interval is desired, such as one NEMA standardequipment mounting space. At various points in the topology (e.g., atplugs or receptacles of the parallel micro-ATS modules 2200, at thehydra cord heads, etc.) locking power cord technologies can be used toimprove the security of power delivery. For example, standard NEMA L5-15locking receptacles for 120V service or NEMA L6-15 receptacles for 200V+service can be used. The “hydra cord head” on the output cords can beequipped with IEC locking receptacles (C13 and C19) using varioustechnologies.

It is worth noting that, although the enclosure 2205 takes up rackspace, it can also eliminate the need for in rack plugstrips 1880, whichare typically mounted vertically in the equipment rack 1875.Accordingly, data center floor space can be optimized by reducing thewidth of each equipment rack 1875. For example, equipment racks 1875 areoften around 27″ wide to allow adequate space to mount a variety ofvertical plugstrips 1880, which do not have industry standardizeddimensions. The NEMA standard equipment width that is most commonly usedis 19 inches. Therefore the total width and depth of the rack determineits floor area usage. By eliminating the need to run anything but powercords and network cords down the sides of the rack, it is possible tospecify narrower racks, down to a width of approximately 21 inches. Forthe sake of illustration, suppose 24-inch wide racks (which would alignonto standard two-foot by two-foot floor tiles used in most raisedfloors) are used instead of 27-inch wide racks. Nine 24-inch racks couldbe deployed in the same floor space that previously accommodated onlyeight 27-inch racks.

It is further worth noting that a typical rack-mountable ATS can causethe entire set of EDP equipment 1885 in the rack to fail if the ATSfails (e.g., as in embodiments of the configuration illustrated in FIG.18C). However, the highly parallel implementation described herein canminimize the domain of failure to only the one (or small subset) ofend-user devices that are powered by each individual micro-ATS 700 inthe parallel micro-ATS module 2200. This can appreciably improvereliability, servicing, etc.

Power distribution topologies, like the ones illustrated in FIGS. 21 and23, provide a number of features. One such feature involves inputvoltage range control. Modern power supplies can tolerate a wide rangeof power quality flaws, but they typically cannot survive lengthy inputpower over-voltage conditions. The TVSS unit 2110 can filter transientsurges and spikes, but it does not compensate for long periods of inputpower over-voltage (i.e., these are passed through to the root nodes).To guard against these conditions, embodiments address out-of-rangevoltages (e.g., modern power supplies are not typically damaged byunder-voltage conditions, but will still shutdown) by switching to theconditioned UPS power if the utility line power voltage goes out ofrange.

A number of techniques are possible for implementing this switching. Forexample, voltage sensing and auto-switching could be implemented atdifferent locations in the data center power system. However, for atleast the reasons discussed above, many of these techniques havesignificant limitations. Accordingly, embodiments typically use one ofthe following techniques.

Some embodiments implement over-voltage protection at the utilitystep-down transformer (e.g., site transformer 2110). Auto-rangingtransformers of this type are available and can often be ordered fromutility companies. Configurations have a set of taps on their outputcoil and automatically switch between them as needed to control theiroutput voltage to a specified range. Step-down transformers of this typeof this type are not usually deployed by utility companies (e.g.,because of cost), but they can often be specified and retrofitted forpower distribution topologies if requested.

Other embodiments implement over-voltage protection at an ATS in thepower distribution topology. As described above with reference to FIGS.18A-18D, 21, and 23, ATSs can be placed in a number of locationsthroughout the topology, for example, including at panelboards, at theend of a branch circuit, at the device level, etc. The powerdistribution topologies shown in FIGS. 21 and 23 illustrate implementingthe switching by placing micro-ATSs 700 at the device level. It shouldbe noted that a semiconductor-based ATS could be used upstream of theUPS, but this can be relatively very expensive, and a failure of the ATScould result in potentially catastrophic effects, as all of the poweredEDP units could have their power supplies damaged or destroyed if theATS unit fails to switch.

Another feature of power distribution topologies using micro-ATSs 700 isthe availability of auto-switching of all single power supply (or cord)EDP devices. If utility line power fails, it is desirable for all singlepower supply EDP devices to be switched to a reliable alternate powersource, such as power supplied via the UPS. EDP equipment 1885 mayrequire that the switching is accomplished within a predeterminedmaximum time (e.g., the CBEMA 20 millisecond guideline). Notably, whileplugging all devices directly into the UPS would provide highly reliablepower, it would also appreciably reduce power distribution efficiencyover any implementation that only uses the UPS during the times whenutility power is down. This can have significant impacts in environmentslike large server farms, where the cost constraints are such that singlepower supply configurations for the massive number of servers aregreatly preferred for cost and efficiency reasons, and services will notbe much or at all interrupted by the loss of a single or a few servers.

Yet another feature of power distribution topologies using micro-ATSs700 is auto-switching of all dual (or N+1) power supplies in EDPdevices. EDP equipment 1885 implemented with multiple power suppliestypically share the load among their available power supplies. It ispossible to build an EDP device that switches the load between powersupplies, so that only one or more are the active supplies and theothers are idle, but as described earlier, this is rarely done for bothcost and reliability reasons. Embodiments ensure that multi-power-supplyEDP equipment 1885 draw on only filtered utility line power if it isavailable (and of sufficient quality) and switch to the UPS only if itis not. To this end, embodiments auto-switch each secondary power supplyunit between the utility line and UPS power. Otherwise, the UPS unitwill bear a portion of the data center load, which can lower the overallefficiency of the power distribution.

Still another feature of power distribution topologies using micro-ATSs700 is avoidance of harmonic reinforcing power load surges. If utilityline power fails, all EDP devices must draw on the UPS unit until thegenerator starts and stabilizes. Modern generators used in data centershave very sophisticated electronics controlling their engine “throttle”.The control logic of the generator is designed to produce maximumstability and optimum efficiency. However, it takes a certain amount oftime to respond to a changed electrical load and then stabilize at thatnew load. If the load put on the generator changes too fast in arepeating oscillation pattern, it is possible to destabilize thegenerator, by defeating its control logic and forcing it to try to matchthe oscillations of the power demands. This can either damage thegenerator or force it to shutdown to protect itself. In either case thedata center can potentially go off-line, which can be a very undesirableresult. There are several potential scenarios that can potentially causethis problem.

One such scenario is when there is an intermittent utility line failure.Utility line power is outside the control of the data center operator.It can be affected by weather, equipment faults, human error and otherconditions. It can fail intermittently which poses a potential hazard tothe core data center power infrastructure. If utility power goes on andoff intermittently, and the timing of the on-off cycles is within acertain range, auto-switching between the utility line source and thegenerator (even filtered by the UPS units) can result in harmonicreinforcing power load surges being imposed on the generator.

For example, suppose utility line power from the site transformer 1815fails. As desired, power is switched to UPS 1835 power. Eventually, atimeout occurs, causing the local generator 1820 to auto-start. When thelocal generator 1820 stabilizes, it may be switched into the system bythe main switch gear 1825, thereby feeding the UPSs 1835. At some point,utility line power returns and then goes off again. The local generator1820 will not have shutdown, but the main switch gear 1825 may nowswitch between the local generator 1820 and site transformer 1815 powersources. Any equipment-level ATSs (e.g., micro-ATSs 700 at the EDPequipment 1885) will return to line power when it is back on. Notably,however, the timing of this return may be critical: if it happens toofast for the local generator 1820 to respond properly, and utility linepower fails in an oscillating fashion, the local generator 1820 maybecome destabilized, as described above.

Another such scenario occurs when there is load/voltage oscillation.When a load is switched onto the local generator 1820, especially alarge load, its output voltage can momentarily sag. The local generator1820 may then compensate by increasing throttle volume and subsequentengine torque, which increases output current and voltage. There aremechanisms to keep the output voltage in a desired range, but they canbe defeated by a load that is switched in and out at just the rightrange of harmonic frequency. This can happen, for example, if the powerdistribution system has protection from overvoltage built into it viamechanisms (e.g., as described below). Again, the result can be harmonicreinforcing power load surges being imposed on the local generator 1820.

For example, suppose again that utility line power from the sitetransformer 1815 fails. As desired, power is switched to UPS 1835 power,a timeout occurs, and the local generator 1820 auto-starts. When thelocal generator 1820 stabilizes, it may be switched into the system bythe main switch gear 1825 (e.g., the local generator 1820 is switchedinto the system to feed the utility line power side of the system inpreference to feeding through the UPS in order to maintain redundantfeeds to the racks w/EDP equipment). The local generator 1820 sags underthe large load suddenly placed on it and may respond by increasing itsthrottle setting. The local generator 1820 overshoots the high voltagecutoff value of the micro-ATS 700 units, causing them to switch back toUPS power, thereby removing the load from the local generator 1820. Thelocal generator 1820 then throttles back and its output voltage returnsto normal levels. The micro-ATS 700 units switch back to the generator,causing it to sag again. The sag and return of the local generator 1820throttle can repeat, causing a harmonic reinforcing power load surge tobuild up and destabilize the local generator 1820.

As discussed above, implementation of a power distribution topologyusing micro-ATSs 700 (e.g., alone or as part of a parallel micro-ATSmodule 2200) involves a number of features, particularly when theimplementation is to include safe, reliable, and economical use offiltered utility line power. These features include input line powervoltage range control, auto-switching of single power cord EDP devices,auto-switching of dual (or N+1) power supply EDP devices, prevention ofharmonic reinforcing load surges. These features can be realized byauto-switching at the device or near-device level in the powerdistribution topology. However, to realize these features, embodimentsof micro-ATSs 700 are used having a number of characteristics. It willbe appreciated that the micro-ATS 700 embodiments described abovemanifest these characteristics either by virtue of their design as asingle micro-ATS 700 embodiment or when combined into a highly parallelATS embodiment (e.g., as part of a parallel micro-ATS module 2200).

Embodiments of the micro-ATS 700 prefer and select the primary powersource (e.g., “A” power 760) when it is available and of sufficientquality. For example, maximum efficiency may be realized by ensuringthat, if utility line power is available and of sufficient quality, itis being used to power all loads.

Embodiments of the micro-ATS 700 also protect against out-of-rangevoltage conditions on the primary power source and switch to thesecondary power source if the primary power source is out of range (andswitch back to the primary source when it returns to the acceptablerange and is stable). It is also desirable that the micro-ATS 700 switchto the secondary power source as a precaution when other primary powersource issues are detected. Some embodiments may not manifest thischaracteristic, as they may exploit the fact that modern power suppliesare relatively immune to power quality issues other than input voltagerange.

Further, embodiments of the micro-ATS 700 transfer within the CBEMA20-millisecond limit in both directions (i.e., from primary to secondarypower and from secondary to primary power). In fact, some embodimentsswitch from “A” power 760 to “B” power 765 in 14-16 milliseconds. Whilecircuit embodiments described above can be configured to achieve evenfaster switching times, switching times are selected also to maximizerejection of false conditions that could initiate a transfer. In someembodiments, transfer times between “B” power 765 and “A” power 760 areapproximately 5 milliseconds once initiated (e.g., after a delay, asdescribed below). For example, this transfer timing can be achievedbecause most “B” power 765 to “A” power 760 transfers occur after “A”power 760 has returned to an operational condition, so that themicro-ATS 700 can select the time to make the transfer when both powersources are up and running.

Embodiments of the micro-ATS 700 also incorporate a delay factor insecondary to primary power switching (except if the secondary powersource fails). The delay factor chosen is sufficient to allow moderngenerators to stabilize their throttle settings and not oscillate. Forexample, the time is selected to be outside of the normal response timecharacteristics of most typical generators to prevent harmonicreinforcing load surges by allowing the generator time to adapt to theload change and to stabilize its output.

Even further, embodiments of the micro-ATSs 700 are configured to useminimal or no valuable rack space that could be used for EDP equipment1885. For example, embodiments mount in a “zero-U” fashion or areotherwise integrated into or near the rack without using rack space.Certain embodiments are integrated into EDP equipment 1885 directly.Other embodiments are integrated into plugstrips 1880 or in-rack ornear-rack power distribution units such as the Zonit Power DistributionUnit (ZPDU). These embodiments may trade a minimal amount of rack spaceusage against access at the rack to the circuit breakers controllingpower to the plugstrips 1880 in the racks. According to certain of theseembodiments, the ATS function is integrated into every sub-branch outputof the local power distribution unit, so that each one is auto-switched.This can be a worthwhile trade-off to some data center managers.

Still further, embodiments of the micro-ATS 700 (e.g., when deployed asparallel micro-ATS modules 2200) also “spread” the load on the sourcebeing transferred. In practice, each micro-ATS 700 has a small degree ofvariability in its timing of transfers from “B” power 765 to “A” power760 with respect to other micro-ATS 700 (e.g., as an artifact of themanufacturing process). The variability is not large in real time but issignificant in electrical event time. When running the micro-ATSs 700 ascomponents of a parallel micro-ATS modules 2200, the variance “spreads”the load being transferred as seen by the power source, for example, agenerator or UPS unit. For instance, the load appears to the powersource as a large number of micro-ATS 700 transfers over a time window.This can be beneficial to generators and UPS units, since it distributesa large number of smaller loads over a period of time, thereby reducinginstantaneous inrush.

Embodiments of the micro-ATS 700 are also highly efficient, reliable,and inexpensive. When deploying micro-ATS 700 units at the device level,there will be a large number of them, and they must therefore beefficient enough to offset the cost of their purchase. Embodiments useless than 100 milliwatts when on the primary power source in normaloperational mode. In a related sense, they must be highly reliable andotherwise inexpensive to purchase.

As discussed above, features of the micro-ATS 700 allow deployment ofdevice-level ATS functionality that is reliable, efficient,cost-effective, and of minimal impact to rack space usage. For reasonsdiscussed above, a population of highly reliable ATS units at the devicelevel can produce much higher per-device power reliability levels thanan ATS that switches a branch circuit or an entire panelboard can. Forexample, the chance that all micro-ATSs 700 will fail at the same timeand affect all their connected, auto-switched EDP devices isinfinitesimal as compared to the chance that a single ATS deployedcloser to the root of the power distribution topology will fail.

Additionally, it is desirable that techniques for data center powerdistribution are highly efficient. Highly parallel implementations ofdevice or near-device level auto-switched power distribution can providea highly efficient approach that is also cost-effective to implement forseveral reasons. As noted above, mechanical relay-based ATSs tend to bemore efficient more reliable (at given cost levels) than solid-statebased ATSs, but they may also exhibit relatively high loss due tocontact resistance and relatively higher relay transfer times. However,using many small ATS units in parallel at the device or near-devicelevel (e.g., as parallel micro-ATS modules 2200) yields an effectivecumulative relay contact area that is much greater than is feasible toput in a higher capacity relay-based ATS unit regardless of where thatunit is placed in the power distribution topology.

Further, deploying the micro-ATS 700 units in parallel micro-ATS modules2200 also allows for a relatively fast transfer time because eachcomponent ATS has smaller relay contacts faster transfer times. It willbe further appreciated that the circuit embodiments described aboveallow the micro-ATS 700 to be more efficient than many traditional ATSunit designs of the same power handling capacity by a factor of 10 ormore. It is worth noting that use of traditional ATS designs in a highlyparallel configuration may not be practical for at least this reason, asthe net result would likely be to consume more power rather than lesspower, regardless of the capital expense of the switching units used.

It will be appreciated that data center power distribution techniquesshould be cost-effective if they are to be widely used and accepted. Asdiscussed above, micro-ATS 700 embodiments are highly cost-effective,due, for example, to relatively low manufacturing costs, relatively longservice life, etc.

A related concern may be preserving rack space wherever possible. Asdiscussed above, space in a data center equipment rack or cabinet can bevery expensive, and embodiments of the micro-ATS 700 can be deployed toconsume little or no rack space (e.g., by being integrated into the rackstructure outside of the volume in the rack where EDP equipment ismounted). For the sake of illustration, suppose a large server farm in adata center has many “pizza-box” servers in a rack with a networkswitch. Each server may use around 3-6 watts of 120-volt power, suchthat a 15-amp ATS can handle 2-4 servers. If the ATS units are 1 Urack-mounted devices, using one ATS for every 3 servers would stillconsume 25% of the rack space. This may typically be too inefficient ause of expensive rack space to be practical. However, use of a parallelmicro-ATS module 2200 would consume much less rack space (e.g., even arack-mounted implementation typically uses a single rack space).

It is worth noting that use of the micro-ATSs 700 (e.g., as part of aparallel micro-ATS module 2200) can also increase efficiency fortraditional power distribution via UPS load shifting. As discussedabove, it is common to share loads when double-conversion UPS units areused in a data center as the power sources (e.g., as illustrated in FIG.19). This is usually due to the nature of the end use equipment havingdual power supplies that distribute the load more or less equally toboth the “A” and “B” power supply inputs. Also, as discussed above, thiscan reduce UPS efficiency, since they are typically loaded at below 50%to provide fully redundant power.

Using large numbers of micro-ATSs 700, it is possible to raise theefficiency of such a power distribution system. All of the electricalload for EDP equipment 1885 in the data center can be “load shifted” viamicro-ATS 700 units onto one of the two UPS units, increasing theefficiency of that UPS unit (e.g., as shown in the UPS efficiency curveshown in FIG. 20). The other UPS unit is at idle and will only be usedif the primary unit fails. The UPS units must be designed to handle thistype of load being immediately placed on them, but almost all modern UPSunits can do this. The result tends to be an increase of approximately3-5% in the efficiency of the data center.

Implementations can be deployed incrementally for each piece of EDPequipment 1885, which can reduce service impacts. In some embodiments,every power supply (or corded) EDP device will be connected via amicro-ATS 700 to the “A” and “B” UPS units. Every dual or N+1 powersupply EDP device will have one power supply connected to the “A” UPSvia a normal power cord, and the second or all other N+1 power supplieswill be connected to the “A” and “B” UPS units via micro-ATS 700 units.Accordingly, when the “A” UPS unit is available, it takes all the load;and when it is not, the “B” UPS carries the load. As discussed above,the micro-ATS 700 units can be deployed at a per-device ratio, or at aratio of one micro-ATS 700 to a low integer number of EDP devices (e.g.,respecting micro-ATS 700 power capacity limits).

It should be noted that while only one pair of UPS units is discussedhere the methodology scales to larger data centers that have many UPSunits deployed in pairs for redundancy. Similarly, the illustrativeembodiments discussed herein show limited configuration options for thesake of clarity. It will be appreciated that embodiments can be adaptedto any number of equipment racks, EDP equipment, ATSs, panelboards,plugstrips, etc.

Various changes, substitutions, and alterations to the techniquesdescribed herein can be made without departing from the technology ofthe teachings as defined by the appended claims. Moreover, the scope ofthe disclosure and claims is not limited to the particular aspects ofthe process, machine, manufacture, composition of matter, means,methods, and actions described above. Processes, machines, manufacture,compositions of matter, means, methods, or actions, presently existingor later to be developed, that perform substantially the same functionor achieve substantially the same result as the corresponding aspectsdescribed herein may be utilized. Also, as used herein, including in theclaims, “or” as used in a list of items prefaced by “at least one of”indicates a disjunctive list such that, for example, a list of “at leastone of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., Aand B and C). Further, the term “exemplary” does not mean that thedescribed example is preferred or better than other examples.Accordingly, the appended claims include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or actions.

What is claimed:
 1. A power relay apparatus for use in a powerdistribution topology for supplying power to electrical devices, saidpower distribution topology comprising: a core infrastructure includingfirst and second power sources; a distribution portion, disposed betweensaid electrical devices and said core infrastructure, including multipledistribution branches; and leaf portions, associated with saiddistribution branches, including said electrical devices, wherein saiddistribution portion and said core infrastructure are disposed upstreamfrom said leaf portions, said power relay apparatus comprising: an arrayof multiple relays connected in parallel between at least one inputpower feed and at least one output power feed, said array havingmultiple input branches associated with said multiple relays, whereineach input branch includes a time-dependent, current-limiting deviceoperationally disposed between a respective relay of said input branchand a respective input power feed of said input branch, said power relayapparatus being disposed in said power distribution topology upstreamfrom at least one of said leaf portions.
 2. An apparatus as set forth inclaim 1, wherein said time-dependent, current-limiting device has afirst impedance at a first time in relation to operation of said relayto induce current flow though said input branch, and a second impedancedifferent from said first impedance at a second time in relation to saidoperation of said relay.
 3. An apparatus as set forth in claim 2,wherein said time-dependent, current-limiting device includes aresistive element having a resistance value that decreases over timeafter initiation of current flow through said element.
 4. An apparatusas set forth in claim 2, wherein said time-dependent, current-limitingdevice has a first effective resistance of greater than zero for a firsttime period after said operation of said relay and has a secondeffective resistance of substantially zero in a second time period aftersaid first time period.
 5. An apparatus as set forth in claim 1, whereinsaid power relay apparatus is disposed in said core infrastructure. 6.An apparatus as set forth in claim 1, wherein said power relay apparatusis disposed between said first and second power sources and site mainswitchgear.
 7. An apparatus as set forth in claim 1, wherein said powerrelay apparatus is disposed in said distribution portion.
 8. Anapparatus as set forth in claim 7, wherein said power relay apparatus isdisposed between site main switchgear and a power distribution unit. 9.An apparatus as set forth in claim 1, wherein said power relay apparatusis disposed between said leafs and a power distribution unit.
 10. Anapparatus as set forth in claim 1, wherein said power relay apparatus isconnected to a power busway.
 11. A method for use in connecting one ormore power sources with one or more loads via a power distributiontopology, said power distribution topology comprising: a coreinfrastructure including said power sources; a distribution portion,disposed between said loads and said core infrastructure, includingmultiple distribution branches; and leaf portions, associated with saiddistribution branches, including said loads, wherein said distributionportion and said core infrastructure are disposed upstream from saidleaf portions, said method comprising the steps of: providing a powerrelay apparatus including an array of multiple relays connected inparallel between at least one input power feed and at least one outputpower feed, said array having multiple input branches associated withsaid multiple relays, wherein, in each relay branch, an impedanceelement is operationally interposed between a respective relay of saidinput branch and a respective input power feed of said input branchduring a first time period in relation to operation of said relay, andsaid impedance element is operationally bypassed during a second timeperiod after said first time period; and disposing said power relayapparatus in said power distribution topology upstream from at least oneof said leaf portions.
 12. A method as set forth in claim 11, whereinsaid power relay apparatus is disposed in said core infrastructure. 13.A method as set forth in claim 11, wherein said power relay apparatus isdisposed between said first and second power sources and site mainswitchgear.
 14. A method as set forth in claim 11, wherein said powerrelay apparatus is disposed in said distribution portion.
 15. A methodas set forth in claim 14, wherein said power relay apparatus is disposedbetween site main switchgear and a power distribution unit.
 16. A methodas set forth in claim 11, wherein said power relay apparatus is disposedbetween said leafs and a power distribution unit.
 17. A method as setforth in claim 11, wherein said power relay apparatus is connected to apower busway.
 18. A power relay apparatus for use in a powerdistribution topology for supplying power to electrical devices, saidpower distribution topology comprising: a core infrastructure includingfirst and second power sources; a distribution portion, disposed betweensaid electrical devices and said core infrastructure, including multipledistribution branches; and leaf portions, associated with saiddistribution branches, including said electrical devices, wherein saiddistribution portion and said core infrastructure are disposed upstreamfrom said leaf portions, said power relay apparatus comprising: an arrayof multiple relays connected in parallel between at least one inputpower feed and at least one output power feed, said array havingmultiple input branches associated with said multiple relays, and logicfor monitoring each branch of said input branches to determine whether acurrent load of said monitored branch falls within an acceptable rangeand disabling said monitored branch if said current load is outside ofsaid acceptable range, said power relay apparatus being disposed in saidpower distribution topology upstream from at least one of said leafportions.
 19. An apparatus as set forth in claim 18, wherein said logicis further operative for switching another input branch from an idlestate to an active state responsive to determining that said currentload of said monitored branch falls outside of said acceptable range.20. An apparatus as set forth in claim 18, wherein said power relayapparatus is disposed in said core infrastructure.
 21. An apparatus asset forth in claim 18, wherein said power relay apparatus is disposedbetween said first and second power sources and site main switchgear.22. An apparatus as set forth in claim 18, wherein said power relayapparatus is disposed in said distribution portion.
 23. An apparatus asset forth in claim 22, wherein said power relay apparatus is disposedbetween site main switchgear and a power distribution unit.
 24. Anapparatus as set forth in claim 18, wherein said power relay apparatusis disposed between said leafs and a power distribution unit.
 25. Anapparatus as set forth in claim 18, wherein said power relay apparatusis connected to a power busway.
 26. A method for use in connecting oneor more power sources with one or more loads via a power distributiontopology, said power distribution topology comprising: a coreinfrastructure including said power sources; a distribution portion,disposed between said loads and said core infrastructure, includingmultiple distribution branches; and leaf portions, associated with saiddistribution branches, including said loads, wherein said distributionportion and said core infrastructure are disposed upstream from saidleaf portions, said method comprising the steps of: providing a powerrelay apparatus including an array of multiple relays connected inparallel between at least one input power feed and at least one outputpower feed, said array having multiple input branches associated withsaid multiple relays, and a monitoring device for monitoring each branchlogic of said input branches to determine whether a current load of saidmonitored branch falls within an acceptable range and disabling saidmonitored branch if said current load is outside of said acceptablerange; and disposing said power relay apparatus in said powerdistribution topology upstream from at least one of said leaf portions.27. A method as set forth in claim 26, further comprising the step ofswitching another input branch from an idle state to an active stateresponsive to determining that said current load of said monitoredbranch falls outside of said acceptable.
 28. A method as set forth inclaim 26, wherein said power relay apparatus is disposed in said coreinfrastructure.
 29. A method as set forth in claim 26, wherein saidpower relay apparatus is disposed between said first and second powersources and site main switchgear.
 30. A method as set forth in claim 26,wherein said power relay apparatus is disposed in said distributionportion.
 31. A method as set forth in claim 30, wherein said power relayapparatus is disposed between site main switchgear and a powerdistribution unit.
 32. A method as set forth in claim 26, wherein saidpower relay apparatus is disposed between said leafs and a powerdistribution unit.
 33. A method as set forth in claim 26, wherein saidpower relay apparatus is connected to a power busway.